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Which prop to use, please help!

Hello fellow Rinker boaters...

New kid on the block here, coming from Holland. I have a question about which prop is best to use for my Rninker 232 BR. Even the official Rinker dealer here in Holland can not give an explicit answer to my question.

We have the Mercruiser 5.0  Thunderbolt 5 ignition in the back. it says it should rev up to about 4400 and 4800 rpm. The former owner did a lot of waterboarding and therefor mounted a 17" hi five prop. In the beginning the boat reached speeds of about 43/44 mph, at the moment it doesn't even reach 37mph. This is tested on flat water, no wind, no passengers, but fully loaded with petrol.

My dealer says it's not good that it doesn't rev up to about 4800 to 5000 rpm, and says it will hurt the engine, and that it will propably use a lot of extra fuel. Strange thing though is, that he can not tell me exactly how to solve this, and they need to do all kinds of testing with several props etc. I can not imagine that they need invent a new wheel, while the wheel is probably already invented. Maybe I need to send Rinker themselves an e-mail? Or maybe somebody here can tell me what prop would be wise to mount.

I'm not interested in waterboarding/skying. I'm looking for the most efficient prop which will give me the highest top speed possible. From the place where we live, we go very often go to Amsterdam city to do some canal cruising. The way to Amsterdam is over open water, and that's why I'm looking for an efficient prop with a high top speed.

Hopefully someone can help!

Thanks in advance

Menno

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    Cableguy GregCableguy Greg Member Posts: 5,016 ✭✭✭✭✭
    Welcome aboard!

    On my old 1998 232cc, with a 5.7L Thunderbolt V and Alpha 1 Gen2 drive, it had a 3 blade 19 pitch prop that came with it. The 3 blade 17 that I had gave it great hole shot, but no top end. If I switched to a 3 blade 21 pitch prop, hole shot sucked and the top end was awesome. It just took a while to get there. I hope this helps...
    2008 280 Express Cruiser, 6.2MPI, B3, Pittsburgh, PA "Blue Ayes"
    Go Steelers!!!
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    canal cruising.... thank God for those "C's"... <span>:smiley:</span>

    all bets are off when twirling that fifth blade... they can push a lot of water for biting plane, but behave like a much higher pitched prop on the top end... I run a five blade currently, but there is no way i would have relied on it to determine which prop to purchase next unless it was another five blade sought.  
    the high five specifically has a smaller diameter than most other props intent to provide the same performance in four or three blades- and we discuss pitch, material, and blades a lot, but that diameter makes a significant impact too- along with cup and rake...
    a guess I would hold firm to for your application is based on more common three blades and all in stainless steel- and in the form of parameters from fast planing and low rpm plane-cruising, to 'slower out of the hole but faster top end'- but both are going to be inside the intended RPM range of the engine...

    a three bladed geometry of the 'mirage' in no more than 21p, but preferably 19 with a diameter of 14 1/8" would be the top of your speed, bottom of your RPM...

    a three blade 'turbo2' from precision in no more than 19p and 14 1/8 diameter has a bit less pitch transition than the mirage and would do well for splitting the difference.  

    a three blade 17p in 14 1/4 in the 'vengeance' geometry would do well for your highest RPM range and your quickest out of the hole and slowest holding plane... 

    but.... am I understanding correctly that your current setup once achieved the RPM's you need but now doesn't?  
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    mennomennesmennomennes Member Posts: 16
    Welcome aboard!

    On my old 1998 232cc, with a 5.7L Thunderbolt V and Alpha 1 Gen2 drive, it had a 3 blade 19 pitch prop that came with it. The 3 blade 17 that I had gave it great hole shot, but no top end. If I switched to a 3 blade 21 pitch prop, hole shot sucked and the top end was awesome. It just took a while to get there. I hope this helps...


    Thanks mate!

    First of all, thanks for the response, much appreciated. Excuse my technical English, it's not that good, but for what i understood, Rinker delivered their 232 with a 3 blade 19"

    What you're actually saying is, that a three blade 21" would give me the highest top possible, but would take out of the water much slower then the high five that is currently mounted right? That would be fine by me, cause I'm looking for a higher top, acceleration is less important to me. A higher cruising speed would be fine too by the way. Somewhere in the regions of 30mph with lesser rpm and more steady in the water....

    Thanks again!

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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    Then you want the 3-blade 21" pitch to put your boat's engine in the correct WOT range, not over rev and burn a ton of extra petrol.
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    mennomennesmennomennes Member Posts: 16
    canal cruising.... thank God for those "C's"... <span>:smiley:</span>

    all bets are off when twirling that fifth blade... they can push a lot of water for biting plane, but behave like a much higher pitched prop on the top end... I run a five blade currently, but there is no way i would have relied on it to determine which prop to purchase next unless it was another five blade sought.  
    the high five specifically has a smaller diameter than most other props intent to provide the same performance in four or three blades- and we discuss pitch, material, and blades a lot, but that diameter makes a significant impact too- along with cup and rake...
    a guess I would hold firm to for your application is based on more common three blades and all in stainless steel- and in the form of parameters from fast planing and low rpm plane-cruising, to 'slower out of the hole but faster top end'- but both are going to be inside the intended RPM range of the engine...

    a three bladed geometry of the 'mirage' in no more than 21p, but preferably 19 with a diameter of 14 1/8" would be the top of your speed, bottom of your RPM...

    a three blade 'turbo2' from precision in no more than 19p and 14 1/8 diameter has a bit less pitch transition than the mirage and would do well for splitting the difference.  

    a three blade 17p in 14 1/4 in the 'vengeance' geometry would do well for your highest RPM range and your quickest out of the hole and slowest holding plane... 

    but.... am I understanding correctly that your current setup once achieved the RPM's you need but now doesn't?  


    Thanks to you too mate, for the response, really appreciate this!

    I have to say, looking at all your technical knowledge, I'm starting to get a bit lost, hahaha. I see a lot of advise to take a stainless steel prop instead of something else, why is that stainless steel so important, it has better characteristic's?

    My official Rinker dealer by the way, advised me to take a 4 blade instead of a 3 blade. according to him this will give better torque and better top, which I think is very strange and contradictive, but again, I have very little knowledge.

    Looking (and hopefully understanding) your information correctly, a 3 blade 21" prop would be the one to look for? highest top, less acceleration right?

    About your last question: as far as I can remember it once did 43/44 mph, and now doesn't even reach 37 mph. But I'm not sure if that is with the same rpm to be honest

    Thanks for the feedback!

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    mennomennesmennomennes Member Posts: 16
    Michael T said:
    Then you want the 3-blade 21" pitch to put your boat's engine in the correct WOT range, not over rev and burn a ton of extra petrol.

    All right, i'll go search for that then. What does wot range mean by the way, I have googled for it, but can't find a descent explanation ;-)
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    chamberbchamberb Member Posts: 265 ✭✭✭
    Wide Open Throttle
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    It is the range your engine's RPM should fall in when the proper propeller is on your specific boat with the load you normally use. You can goggle your engine on the internet to find its proper RPM range at WOT or wide open throttle. Then it's just a matter of selecting the correct propeller to put your engine/boat package in that range. As a rule 1" pitch up decreases rpm by 200 while one I" of pitch down increases RPM by 200.
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    mennomennesmennomennes Member Posts: 16

    chamberb said:
    Wide Open Throttle

    Thanks!
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    mennomennesmennomennes Member Posts: 16

    This is the prop I was looking for earlier, but it's aluminium instead of stainless steel......bad idea to buy this you guys think?

    https://bootplus.nl/alpa/6517-3-blads-aluminium-mercruiser-alpha-one-powertech.html 

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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    I have no problems with aluminum props unless you are going high performance - which you aren't. I like that aluminum will bend if it hits a rock and is cheap to fix whereas SS hits a rock it can bend your drive shaft and crack gears and is a pita to fix and $$$$. I'd get the aluminum one and if you like it and still want an SS then get one later and keep the alum. for a spare or sell it. That's my 2 cents.
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    chamberbchamberb Member Posts: 265 ✭✭✭
    No problem. Welcome to the forum! PS cruising the canals in Amsterdam.... Nice!
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    mennomennesmennomennes Member Posts: 16
    Michael T said:
    I have no problems with aluminum props unless you are going high performance - which you aren't. I like that aluminum will bend if it hits a rock and is cheap to fix whereas SS hits a rock it can bend your drive shaft and crack gears and is a pita to fix and $$$$. I'd get the aluminum one and if you like it and still want an SS then get one later and keep the alum. for a spare or sell it. That's my 2 cents.


    Solid info Michael, thanks! makes a lot of sense too.....by the way, about your earlier response, see below, I have a question. Currently I drive a high five prop with a very small 17". Shouldn't my RPM be on the high side instead of the low side? it rev's about 4400 to 4500 rpm. but with a pitch as small as this, the rpm's should go bazerk isn't it (more in the range of 5000 rpm's)?

    .....It is the range your engine's RPM should fall in when the proper propeller is on your specific boat with the load you normally use. You can goggle your engine on the internet to find its proper RPM range at WOT or wide open throttle. Then it's just a matter of selecting the correct propeller to put your engine/boat package in that range. As a rule 1" pitch up decreases rpm by 200 while one I" of pitch down increases RPM by 200

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    mennomennesmennomennes Member Posts: 16
    chamberb said:
    No problem. Welcome to the forum! PS cruising the canals in Amsterdam.... Nice!

    cheers, thanks, and indeed, canal cruising Amsterdam is great to do!
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    if you were once getting 4400 to 4800 RPM with your current engine and prop combination and there is no damage to the prop or growth on the hull, I'd be leaning more to concern as to why the engine isn't performing anymore....

    when was your last tune up?  Wires? Plugs? Distributor cap? Fuel filter? Do you have stretch in your throttle cable that limits your throttle range? Are your trim sensors functional and accurate, do you trim based on feel or sight of the gauge?  what temperatures are you seeing? If carb'd, is your choke stuck? is there any smoke or smell of unburnt fuel in your exhaust?  is the inner part of your props hub black or slightly rust discolored? 

    but sticking with the prop theme:  the high five is in a class of its own and makes comparing other props difficult, especially when trying to size/pitch based off of its performance... 

    which five do you have?  one is 13 3/8" and the other is 12 3/4 inch in diameter... the smaller one is intended for small gear case outboards, but will fit on an out drive... you'll be able to spin that one a lot faster than the larger one (making RPM's), but it will slip a LOT, and not produce top end speed.  the larger one will bite hard and bring you on plane quickly, and it won't slip on the top as badly as the smaller one- but you won't see the higher RPM's as it's loading the engine more.  

    If I were you, and I'm not- but if I were, I'd fully tune the engine and replace all filters (air and fuel) before I shopped for props- it likely needs to be done if you purchase a new prop or not. 

    You may be able to spin a 21p 14 inch+ prop to 4400-4800RPM with that boat, but I doubt it- I'd think a 19p is likely as large as you'll want to go... if you're looking for top end as you've indicated, a three bladed prop in the geometry of a mirage, turbo2, or stiletto may do you justice...  I'm a bit partial to the Turbo2 geometry, as it is nicely progressive pitched (19p being the average; the leading edge being likely 18p which is where the water cuts out of the hole, and likely 20p on the trailing edge where the cut is on plane), not too dramatically raked (bow doesn't ride too high nor too low)... you MAY be able to twirl a 21p if it is vented but it's a risk...  
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    mennomennesmennomennes Member Posts: 16
    if you were once getting 4400 to 4800 RPM with your current engine and prop combination and there is no damage to the prop or growth on the hull, I'd be leaning more to concern as to why the engine isn't performing anymore....

    when was your last tune up?  Wires? Plugs? Distributor cap? Fuel filter? Do you have stretch in your throttle cable that limits your throttle range? Are your trim sensors functional and accurate, do you trim based on feel or sight of the gauge?  what temperatures are you seeing? If carb'd, is your choke stuck? is there any smoke or smell of unburnt fuel in your exhaust?  is the inner part of your props hub black or slightly rust discolored? 

    but sticking with the prop theme:  the high five is in a class of its own and makes comparing other props difficult, especially when trying to size/pitch based off of its performance... 

    which five do you have?  one is 13 3/8" and the other is 12 3/4 inch in diameter... the smaller one is intended for small gear case outboards, but will fit on an out drive... you'll be able to spin that one a lot faster than the larger one (making RPM's), but it will slip a LOT, and not produce top end speed.  the larger one will bite hard and bring you on plane quickly, and it won't slip on the top as badly as the smaller one- but you won't see the higher RPM's as it's loading the engine more.  

    If I were you, and I'm not- but if I were, I'd fully tune the engine and replace all filters (air and fuel) before I shopped for props- it likely needs to be done if you purchase a new prop or not. 

    You may be able to spin a 21p 14 inch+ prop to 4400-4800RPM with that boat, but I doubt it- I'd think a 19p is likely as large as you'll want to go... if you're looking for top end as you've indicated, a three bladed prop in the geometry of a mirage, turbo2, or stiletto may do you justice...  I'm a bit partial to the Turbo2 geometry, as it is nicely progressive pitched (19p being the average; the leading edge being likely 18p which is where the water cuts out of the hole, and likely 20p on the trailing edge where the cut is on plane), not too dramatically raked (bow doesn't ride too high nor too low)... you MAY be able to twirl a 21p if it is vented but it's a risk...  


    Holy **** man, this is way to much technical info for me, I'm lost. All I know is that the official Rinker dealer takes it out of the water each autumn, where it will be stalled in a warmed storage. At the same time they clean the complete haul of the boat and service the engine replacing everything that is necessary. It's the yearly maintenance treat when the boat is out of the water. they put cooling liquid in the cooling system too, preventing it from corrosion and stuff.

    As far as I can remember, the engine never reved up above 4400 tot 4500 rpm. but the top speed was higher in the beginning. So I'm thinking the prop is damaged? Stretch in the throttle cable? have no idea, but it might be something to check out. I trim based on feeling, while checking the GPS speed. Temperatures are normal. It doesn't smoke, only when starting up the engine sometimes, depending on how much fuel I pump into the carburettors. If it smokes, it disappears after a few seconds, when all the fuel is burned up, after that absolutely no smoke visible. The inner part of the prop needs to be checked, but the prop certainly is not new anymore. There is even a a little dent/curve on one of the blades on the far end. So it needs to replaced anyways, it's damaged here and there. but I definitely do not want a high five (or 5 blade at all). it's to nervous, and especially in corners it becomes bity on hand, and sometimes very slippery, losing all grip at a sudden. when I trim down a little, the grip returns.

    I have no idea what size my prop has, but I send that question my dealer already. All I know is that it's a 17", making it the smallest high five there is, my dealer told me. I still try to figure out what the difference is between pitch and inch on a prop. Inch is probably about the diameter of the prop, where pitch tells me something about the distance from the beginning of each blade to the far end of the tip of the blade, also giving me the exact number of the curve of the blade, or am I totally wrong?

    Best regards

    Menno (and thanks again!)

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    edited April 2016
    pitch= the distance the prop will move the boat forward if there is zero slip and one revolution of the prop.  higher numerical pitch is like using a wood screw- every rotation moves the head of the screw dramatically closer to seat, where using a lower numerical rated pitch is like using a machine screw- it takes far less power to turn it, but it takes a lot more turns to bring the head to seat.... every inch in pitch is worth about 200rpm on most prop/engine combinations... higher pitch, less RPM... lower pitch, more RPM. 

    diameter is from tip of blade to tip of opposing blade. 

    rake is apparent while looking at the side profile of the prop- how close to the front of the hub (leading edge) the blade starts, and how far it leans backward toward or even past the trailing edge of the hub.  lack of rake will keep your bow planted low at plane, where a lot of rake will lift your bow.  

    geometry is a catch all, but primarily points to the transition of pitch from the base of the blade (where it attaches to the hub) to the tip of the blade.  the average pitch is usually the printed pitch- some props, such as the michigan wheel apollo ( i think that is right) has very little transition- it is almost the same pitch from base of blade to tip.  Others, such as mirage, turbo, ect, have a drastic transition and may be 19p at the base of the blade but aggressively bend to a total of 22.5p at the tip- and averaging 21p...  the idea is that the initial bite into the water cuts where the hub and blade join and transitions down the blade as speed increases- aggressive geometry is for a wider purpose prop, where simple geometry is for singular purpose such as towing at a specific speed range.  

    cupping 'flips' the water off the face of the blade at an angle greater than the blade itself, lessening slippage.  it's almost like 'follow through' when a boxer throws a punch.  

    venting the prop speaks of props with exhaust running through them and out the trailing edge... the idea is to have holes in the barrel of the hub, near the leading edge and between the blades bases... at idle and below planing speed the exhaust is allowed to escape those holes as opposed to all of it coming out the trailing edge- which pushes air (exhaust gasses) into the very water the prop is twirling in- lessening the grip, and allowing a vented prop to turn easier... this allows a boater to use a prop that is a higher pitch than they usually could for the weight of the weight of the boat or the power of the engine... when speed is increased, the tension of water over the vent holes becomes to strong and it disallows the exhaust to continue venting through them- forcing all of the exhaust out the trailing edge of the prop exclusively. 

    stainless steel props flex very little, and will usually get the best of debris they encounter... aluminum props flex like mad, and won't survive most encounters with debris... if you run in waters with hard obstacles, i'd rec an aluminum prop and be ready to replace it... the aluminum prop is almost disposable in this regard... if you run in waters where most obstacles are soft (such as sand), I'd rec a stainless prop- but one with a well designed hub that will break/slip instead of breaking your gear case as a result of hitting something hard... stainless props are heavier and take more energy to spin, and they don't flex much if at all- it will cost your engine likely 50-100RPM to spin a stainless... aluminum will spin faster based on it's weight, but it will flex into a geometry below it's rated pitch while doing so- accounting for that 50-100RPM gain in engine RPM over the same prop in stainless. 

    seriously... ^ that is all you really need to know about props to make an informed choice...  


    don't fear the fifth blade- the Ron Hill Pleasure Five in 19p, which I run currently, is never coming off my boat... it is fantastic- silly low slippage, like 4% is all... great pulling power and hole shot? what is 'the hole'? my boat is on plane in the length of the boat- not exaggerating... the bite in turns is astounding... low speed handling is impressive... reverse bites just as strong as forward.  I can plane at ridiculously low RPM, but I can nail the proper range at WOT...  That 'high five' may be the most popular five blade, but it is likely the worst one out there... with Mercury's name behind it, it has done well... the Ron Hill Five is ten times the prop...

    that said- four blades are going to be slightly slower top end than three blades... four blades will lift the stern higher than three blades, and usually drops the bow lower than three blades...

    three blades usually moves faster than four blades, drops the stern compared to four blades, and lifts the bow higher compared to four blades... they have potential to slip more than four blades, and they don't have the 'bite' four blades have in rough seas or while pulling/towing.  

    there isn't a prop that is going to do everything as good as another... unless you have but one express purpose for your boat- and I don't know anyone that does.  

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    mennomennesmennomennes Member Posts: 16
    pitch= the distance the prop will move the boat forward if there is zero slip and one revolution of the prop.  higher numerical pitch is like using a wood screw- every rotation moves the head of the screw dramatically closer to seat, where using a lower numerical rated pitch is like using a machine screw- it takes far less power to turn it, but it takes a lot more turns to bring the head to seat.... every inch in pitch is worth about 200rpm on most prop/engine combinations... higher pitch, less RPM... lower pitch, more RPM. 

    diameter is from tip of blade to tip of opposing blade. 

    rake is apparent while looking at the side profile of the prop- how close to the front of the hub (leading edge) the blade starts, and how far it leans backward toward or even past the trailing edge of the hub.  lack of rake will keep your bow planted low at plane, where a lot of rake will lift your bow.  

    geometry is a catch all, but primarily points to the transition of pitch from the base of the blade (where it attaches to the hub) to the tip of the blade.  the average pitch is usually the printed pitch- some props, such as the michigan wheel apollo ( i think that is right) has very little transition- it is almost the same pitch from base of blade to tip.  Others, such as mirage, turbo, ect, have a drastic transition and may be 19p at the base of the blade but aggressively bend to a total of 22.5p at the tip- and averaging 21p...  the idea is that the initial bite into the water cuts where the hub and blade join and transitions down the blade as speed increases- aggressive geometry is for a wider purpose prop, where simple geometry is for singular purpose such as towing at a specific speed range.  

    cupping 'flips' the water off the face of the blade at an angle greater than the blade itself, lessening slippage.  it's almost like 'follow through' when a boxer throws a punch.  

    venting the prop speaks of props with exhaust running through them and out the trailing edge... the idea is to have holes in the barrel of the hub, near the leading edge and between the blades bases... at idle and below planing speed the exhaust is allowed to escape those holes as opposed to all of it coming out the trailing edge- which pushes air (exhaust gasses) into the very water the prop is twirling in- lessening the grip, and allowing a vented prop to turn easier... this allows a boater to use a prop that is a higher pitch than they usually could for the weight of the weight of the boat or the power of the engine... when speed is increased, the tension of water over the vent holes becomes to strong and it disallows the exhaust to continue venting through them- forcing all of the exhaust out the trailing edge of the prop exclusively. 

    stainless steel props flex very little, and will usually get the best of debris they encounter... aluminum props flex like mad, and won't survive most encounters with debris... if you run in waters with hard obstacles, i'd rec an aluminum prop and be ready to replace it... the aluminum prop is almost disposable in this regard... if you run in waters where most obstacles are soft (such as sand), I'd rec a stainless prop- but one with a well designed hub that will break/slip instead of breaking your gear case as a result of hitting something hard... stainless props are heavier and take more energy to spin, and they don't flex much if at all- it will cost your engine likely 50-100RPM to spin a stainless... aluminum will spin faster based on it's weight, but it will flex into a geometry below it's rated pitch while doing so- accounting for that 50-100RPM gain in engine RPM over the same prop in stainless. 

    seriously... ^ that is all you really need to know about props to make an informed choice...  


    don't fear the fifth blade- the Ron Hill Pleasure Five in 19p, which I run currently, is never coming off my boat... it is fantastic- silly low slippage, like 4% is all... great pulling power and hole shot? what is 'the hole'? my boat is on plane in the length of the boat- not exaggerating... the bite in turns is astounding... low speed handling is impressive... reverse bites just as strong as forward.  I can plane at ridiculously low RPM, but I can nail the proper range at WOT...  That 'high five' may be the most popular five blade, but it is likely the worst one out there... with Mercury's name behind it, it has done well... the Ron Hill Five is ten times the prop...

    that said- four blades are going to be slightly slower top end than three blades... four blades will lift the stern higher than three blades, and usually drops the bow lower than three blades...

    three blades usually moves faster than four blades, drops the stern compared to four blades, and lifts the bow higher compared to four blades... they have potential to slip more than four blades, and they don't have the 'bite' four blades have in rough seas or while pulling/towing.  

    there isn't a prop that is going to do everything as good as another... unless you have but one express purpose for your boat- and I don't know anyone that does.  


    All right, that is definitely to much info for me, I'm dazzling now :) To make things less complex, I need a prop that gives me good cruising characteristics. We normally do a lot of relaxed cruising. just a couple of hundred rpm's above idle. Or I like to go at it's most efficient higher speed with as less rpm's as possible. I don't need a high performance, well manoeuvring and cutting corner's boat. I want a relaxed cruising prop, with (if needed) a high top speed and which is not so nervous as the current one. I think, considering all the info above, 3 blade is the way to go. Now I only need to find out about the pitches and the inches.

    Thanks for the above again, very educating, though I'm still spinning around, hahaha .... 

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    edited April 2016
    well... dang... here comes the punch line: 

    RPM's have less to do with fuel use than would be expected... 

    a prop allowing you to hit near your rev limiter (5200RPM) but where you've throttled back to 4800RPM is using less fuel than a prop only allowing you to hit 4400RPM.... it has to do with load on the engine... the WOT of 4400RPM has the engine delivering all the fuel it possibly can, but is loading the engine (due to resistance) to where it can't achieve the higher RPMs... 

    your engine is designed to operate comfortably at a ceiling of 4800RPM WOT... and at a bottom of 4400RPM while under WOT... anything more threatens valve float, and the power curve due to the camshafts profile falls off after 5kRPM anyway... anything less than WOT of 4400RPM is overloading the engine and hard-on outdrives, cranks, pistons and connecting rods, bearings (as you can imagine) and valve faces- especially valves...

    whatever prop you choose needs to be capable of pushing your boat to the expected range of RPMs... the closer to the top of that range, the safer... 

    You likely should consider a 19P prop of at least 14" diameter... three or four blade, and based on your last post I four blade as it generally provides a lower planing speed and doesn't lose much off the top end if any. 

    I'm not trying to kill you with text/type and technical stuff, I'm trying to help you understand the relationships between your engine, your outdrive, your prop, and what the three of them are pushing (actually, it's pulling, but that's another tale for later)...  :)

     
    Post edited by raybo3 on
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    mennomennesmennomennes Member Posts: 16
    well... dang... here comes the punch line: 

    RPM's have less to do with fuel use than would be expected... 

    a prop allowing you to hit near your rev limiter (5200RPM) but where you've throttled back to 4800RPM is using less fuel than a prop only allowing you to hit 4400RPM.... it has to do with load on the engine... the WOT of 4400RPM has the engine delivering all the fuel it possibly can, but is loading the engine (due to resistance) to where it can't achieve the higher RPMs... 

    your engine is designed to operate comfortably at a ceiling of 4800RPM WOT... and at a bottom of 4400RPM while under WOT... anything more threatens valve float, and the power curve due to the camshafts profile falls off after 5kRPM anyway... anything less than WOT of 4400RPM is overloading the engine and hard-on outdrives, cranks, pistons and connecting rods, bearings (as you can imagine) and valve faces- especially valves...

    whatever prop you choose needs to be capable of pushing your boat to the expected range of RPMs... the closer to the top of that range, the safer... 

    You likely should consider a 19P prop of at least 14" diameter... three or four blade, and based on your last post I four blade as it generally provides a lower planing speed and doesn't lose much off the top end if any. 

    I'm not trying to kill you with text/type and technical stuff, I'm trying to help you understand the relationships between your engine, your outdrive, your prop, and what the three of them are pushing (actually, it's pulling, but that's another tale for later)...  :)

     


    Okay, so you think a 21 pitch would be to high anyways? what I find remarkable by the way, is that my dealer says a 17" is really small, and now you even think a 19 pitch, 14" prop might do the trick......geeee man, that comes as a surprise.

    I know you're trying to help, which is very much appreciated! About the pulling instead of the pushing, I think I know what you mean there. same with airplanes, they don't fly on top of the air, they get sucked into the air ;-)

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    edited April 2016
    yup... that prop is a screw that drives itself into the water- it pulls itself along more than it pushes itself.... 

    anyway...

    it sounds counter intuitive, but sometimes a lower pitched prop will outrun a higher pitched prop even at near the same RPM's, and because of slippage... the higher pitch prop is trying to bite too much in this instance, and something has to give- so it breaks free and spins in it's own little capsule of water every 1/3 turn, say from 1 to 3 o'clock... where as the lower pitch is biting nicely all the way around the clock, but the engine lacks power to turn it any faster... 

    you'll find you'd rather have the lower pitched prop more often than the higher- especially if you are off plane (in the canals maybe?) and putzing around... higher pitched props move the boat further forward for every spin, and can make idle speed maneuvering difficult, and a one hand on the wheel one hand on the shifter circumstance as you have to constantly bump into and out of gear... a lower pitch bites nicely, offers better handling, and a slower speed at idle... that's a big deal to me, and it may be to you, too. 
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    mennomennesmennomennes Member Posts: 16
    edited April 2016
    yup... that prop is a screw that drives itself into the water- it pulls itself along more than it pushes itself.... 

    anyway...

    it sounds counter intuitive, but sometimes a lower pitched prop will outrun a higher pitched prop even at near the same RPM's, and because of slippage... the higher pitch prop is trying to bite too much in this instance, and something has to give- so it breaks free and spins in it's own little capsule of water every 1/3 turn, say from 1 to 3 o'clock... where as the lower pitch is biting nicely all the way around the clock, but the engine lacks power to turn it any faster... 

    you'll find you'd rather have the lower pitched prop more often than the higher- especially if you are off plane (in the canals maybe?) and putzing around... higher pitched props move the boat further forward for every spin, and can make idle speed maneuvering difficult, and a one hand on the wheel one hand on the shifter circumstance as you have to constantly bump into and out of gear... a lower pitch bites nicely, offers better handling, and a slower speed at idle... that's a big deal to me, and it may be to you, too. 


    Check, and it will still give me a nice top speed too? cause that 's another deal breaker for me. Considering the info you gave me in your last post, I need all those things in that prop indeed, and on top that a high top speed, then I'm really okay!

    Can I ask you by the way, where in the heII did you get all this knowledge and info. It's really starting to make sense to me now

    Post edited by raybo3 on
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    choosing a prop on the lower pitched side of the RPM range (allowing higher RPM's) is the safer bet for your engine, and it will make your boating more enjoyable except for all out top speed- which ought to be only a brief thing from time to time unless your engine is made for it... which would be impractical in any rinker made- they aren't made for speed, but enjoying a relaxing pace and having enough power/speed to get you out of trouble when required.  

    that is the true reason to want the speed and power... there isn't a fear I've encountered like facing 5 foot+ short frequency waves out of the trough of one you just negotiated, and not knowing if you have the power to get up the face before it crests- and with your family in the boat... just me? HELZ YEAH!!! With them? PUCKER FACTOR x 1k.... the ocean around here can do that out of nowhere.  likewise- outrunning a storm: it's nice to go to WOT and have your prop married properly to your boat, and right at the ceiling of your recommended RPMs,- knowing your engine may not like you much when you get home, but that it is more than likely a certainty that it's actually going to get you home as fast as it (and you) safely can is a dang comforting thought process in such circumstances... it's also reassurance that you're operating your boat within the parameters engineers expected you to, and you aren't slowly beckoning catastrophic failure by asking something from it that it isn't designed to do. 

    there is a lot of knowledge on this forum... I knew nothing when I got here... hang around- these old geezers have some good knowledge to share- you'll have to stick around long enough to discern when they're sober and when their in port... Diesel Steve and MT get sideways and talk madness when they've been in the canteen too long, and resort to conversations that mean nothing to anyone who don't run diesels... 

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    Dream_InnDream_Inn Member, Moderator Posts: 7,590 mod
    Menno, welcome to the forum.  As you see there is a ton of knowledge here and don't let 212row fool you, he was quite knowledgeable when he joined this forum.  Not sure who he is calling old geezers though.  (must be that diesel guy!)

    Dream 'Inn III -- 2008 400 Express

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    Handymans342Handymans342 Member Posts: 10,375 ✭✭✭✭✭
    Really guys, Really ??????????!!!!!!! LOL
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    .....yes Steve - really.....and you know it always will be 'cuase it's soooo much fun!
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    @mennomennes.....sorry I missed your second question. Your RPM/MPH calculations  of 200RPM change for 1" pitch ONLY hold true if you are comparing the exact same "style" of propeller. IF you change the number of blades (like from a 3 blade to a 4 blade or high five), the diameter, the rake or the cup you have to recalculate as that completely changes your comparison profile - does that explanation make sense to you?
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    mennomennesmennomennes Member Posts: 16
    Michael T said:
    @mennomennes.....sorry I missed your second question. Your RPM/MPH calculations  of 200RPM change for 1" pitch ONLY hold true if you are comparing the exact same "style" of propeller. IF you change the number of blades (like from a 3 blade to a 4 blade or high five), the diameter, the rake or the cup you have to recalculate as that completely changes your comparison profile - does that explanation make sense to you?


    Thanks Michael! As a matter a fact i think all this technical English information is making me dazzle a bit. What probably is going to happen, is that I will be going from a five blade to a three blade. the high five stainless steel is to nervous and bity imo. Especially in corners it feels quite unforgiving, until it suddenly loses grip. I have to trim it down back and then it suddenly grips again. I don't know, from day one I have the feeling that this prop and the boat are not a happy marriage.

    I would like to have it more cruis'n character, and a more smooth and higher top speed, without becoming so jumpy. The propdealer asked me for specific specifications to make a calculation as good as possible. It looks like I have just have to go with that flow and hope that the calculations will be correct for my boat and it will turn out for the best.

    Once I got the info/calculations back from the prop dealer, I will share this with you guys here. Hopefully today or tomorrow I will know more..

    Menno    

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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭

    I tried a high five on my 383 bravo 1 combination and it was a piece of garbage! It had a huge bite to start off but felt "off" during cornering, like it was slipping sideways and sort of skipping.

    At higher speeds the high5 felt very dangerous as It did not feel stable. I took it back and bought a 3 blade 23" pitch SS and the boat was amazing. I sold it many years ago but the owner still uses that prop. He told me he tried 4 or 5 props but liked it best and still uses that prop!

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    mennomennesmennomennes Member Posts: 16
    Michael T said:

    I tried a high five on my 383 bravo 1 combination and it was a piece of garbage! It had a huge bite to start off but felt "off" during cornering, like it was slipping sideways and sort of skipping.

    At higher speeds the high5 felt very dangerous as It did not feel stable. I took it back and bought a 3 blade 23" pitch SS and the boat was amazing. I sold it many years ago but the owner still uses that prop. He told me he tried 4 or 5 props but liked it best and still uses that prop!


    That is some solid feed back Michael! exactly my feelings too about the 5 blader. It has to go anyways, it's time for something else! So 3 blade probably will be satisfying to my needs. Pitch 23 probably will be a bit too much for the "only" 5.0 Mercruiser? Probably need more horse power for the 23 Pitch? What was the inch of that 23 pitch by the way, you remember that?

    Great response Michael, thanks!

    Menno

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