Proper RPM range

CnCCnC Member Posts: 142 ✭✭
edited July 2021 in General Boating Discussions
Wondering if anyone with a (2001) 340 FV can tell me the WOT range would be on our twin Merc 5.7 EFI's with Bravo III's 24 pitch Mercury props? I had it at 48mph GPS at 4200rpm's with more throttle to go? Does that seem like the right figure? Also sorry for the image coming in 3 times!
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  • Handymans342Handymans342 Member Posts: 10,375 ✭✭✭✭✭
    What’s your motors specs?
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  • YYZRCYYZRC Member Posts: 5,464 ✭✭✭✭✭
    edited July 2021
    My boat will barely do 48km/h!! Really tho, that sounds fast for a 340. 

    My 350 with essentially the same motors and 20p 4x4 props runs at 60km/h flat out 5000 rpm
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • CnCCnC Member Posts: 142 ✭✭
    I did think 48mph was a bit high judging by other numbers posted here. I don't want to blow anything up. Where could I find the engine specs @Handymans342 ?
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  • PickleRickPickleRick Member Posts: 4,371 ✭✭✭✭✭
    edited July 2021
    Were your rpms read from the tachometer or do you have a vessel view/ other engine scan tool that will read rpm? Just in case your gauge is off a bit.    


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  • CnCCnC Member Posts: 142 ✭✭
    No not any special vessel view or anything but both RPM gauges were reading 4200rpm's and sync'd at even on that gauge as well? I guess its possible for both tach's to be a bit off?
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  • Handymans342Handymans342 Member Posts: 10,375 ✭✭✭✭✭
    Its on the Mercury tag on the motor
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  • LaReaLaRea Member, Moderator Posts: 8,070 mod
    Might be over-propped.  Does she struggle to get on plane with passengers aboard?  A shorter pitch might help you plane faster without sacrificing top speed.  

    If you are satisfied with the time to get on plane, don't change anything!
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  • Handymans342Handymans342 Member Posts: 10,375 ✭✭✭✭✭
    Does anyone have a pic of the tag on their motor. It shows model, serial and HP at RPM. I believe
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  • PickleRickPickleRick Member Posts: 4,371 ✭✭✭✭✭
    Isn't the max rpm supposed to be around 4800 on those motors?  Your serial number would help very as the rpm range varied a bit over the years.

    Seems like its plenty fast to me! 
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  • aero3113aero3113 Member Posts: 9,853 ✭✭✭✭✭
    4800-5200
    2008 330EC
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  • PickleRickPickleRick Member Posts: 4,371 ✭✭✭✭✭
    edited July 2021
    Well he has more throttle to go...how close can you get to 40 mph?  That's kind of like having a really fast water front condo.  If you hit that magic 4800 id say You're perfect and leave it alone.


    Although I might add that the hill marine 4 blade prop on my bravo 2 worked miracles on my plane time and lowered my cruising...er plowing the water rpms.
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  • YYZRCYYZRC Member Posts: 5,464 ✭✭✭✭✭
    I assume the boat came with 22p props from the factory?
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • aero3113aero3113 Member Posts: 9,853 ✭✭✭✭✭
    I can reach 40 maybe a tiny bit more at 5000 with my 4x4 20P props.
    2008 330EC
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  • YYZRCYYZRC Member Posts: 5,464 ✭✭✭✭✭
    Same as @aero3113 in my 330 and 350. 
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • PickleRickPickleRick Member Posts: 4,371 ✭✭✭✭✭
    aero3113 said:
    I can reach 40 maybe a tiny bit more at 5000 with my 4x4 20P props.
    That's stupid quick for such a big boat. Im always impressed with how efficient rinker made those hulls.  You'd think a big block would be needed to get a boat that's gotta be well above 10,000-12000 lbs to reach 40 mph.


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  • aero3113aero3113 Member Posts: 9,853 ✭✭✭✭✭
    I think my 330 is 16,000 lbs
    2008 330EC
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  • YYZRCYYZRC Member Posts: 5,464 ✭✭✭✭✭
    The 350 is 15500 dry. 
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • PickleRickPickleRick Member Posts: 4,371 ✭✭✭✭✭
    8 tons going 40 mph with a couple small blocks.  I am not that old but I remember when 40 was fast for a jet ski. 
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  • CnCCnC Member Posts: 142 ✭✭
    @LaRea yes it does take a bit to get up on plane which I'd really like to change. My days of trying to go fast and get more speed while on the water ended with Jasper (the name given to my Stratos bassboat by my wife- also referred to her as my mistress). She said I needed less hobbies so here I am pestering all of you. Trading props on my Optimax I suspect will be a whole lot easier on my wallet since there was only one but it is what it is. I can say that I was kinda surprised to see how well it handled after noticing the GPS at 48mph though. Gotta give the designers at Rinker a thumbs up on this. I'm curious now (not that I'll try it) what the other 1000 or so rpm's would have brought the speed to. Since I'm now running 24's would I be way off base to think of dropping to maybe 22's for better planing or is 2 points way too much on these cruisers if I pay more attention to my RPM's? I wouldn't have thought twice about doing it on my outboard but these marine 350's are new to me. 
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  • CnCCnC Member Posts: 142 ✭✭
    One other thing I'd like to add/ask is what do you guys feel is a decent cruising speed and RPM range that I should shoot for? So far I've been running around 40-42mph at 3800-4000 rpms. I feel like I've needed to keep it at around this because coming down in RPMs much more than 3500 or so and it feels like its going to come off plane. Once again all of this is new to me coming from my previous boat
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  • YYZRCYYZRC Member Posts: 5,464 ✭✭✭✭✭
    With no tabs I can’t run below 3900 without dropping off plane. I typically run 4100-4300 at 46-50km/h depending on boat weight and chop. That’s with 20p 4x4 props which are said to be the same as 22p 3x3. 
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • GrahamuGrahamu Member Posts: 921 ✭✭✭
    With my 2006 342 FV I cruise at 3500 RPM, 26 MPH, 22 GPH with tabs down. I very rarely go above 3700 RPM. Twin 5.7 L MPI with standard Mercury dual props.
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  • CnCCnC Member Posts: 142 ✭✭
    edited July 2021
    Great now I'm getting some well needed info. Tell me more about setting these tabs while cruising. What I've been doing is putting them all the way up after getting up on plane so no wonder I'm having to run at 3/4 throttle to keep it there. I've been setting the trim on my outdrives to keep it there
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  • GrahamuGrahamu Member Posts: 921 ✭✭✭
    I'm probably very different to others on this site. I put my tabs all the way down  leaving the dock and leave them there, I find it keeps the boat tracking in a straight line much better than with them up at lower RPM.  At 3200 RPM I'm starting to plane  and at 3500 I'm almost flat and back off the throttles to maintain that RPM. 26 MPH is plenty fast enough for me and I can cruise for a few hours at that setting. I have yet to go above 4000 RPM.
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  • CnCCnC Member Posts: 142 ✭✭
    Thanks @Grahamu this gives me a baseline to start with. As I mentioned speed is of no importance to me and cruising at 25-30mph is a good enough for me. What do you have for props?
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  • GrahamuGrahamu Member Posts: 921 ✭✭✭
    @CnC, I'm not sure of the size but they are Mercruiser Bravo 3 standard 3 blade dual props.
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  • SpyderwebSpyderweb Member Posts: 959 ✭✭✭
    Guys, any possibility the gps is giving bad numbers?  With same engines as @CnC, running 3800-4000, I’m around 28-30 mph.  And same as @CnC, at 3500 (with tabs up) I feel like I’m falling off plane.  Looking at boat test numbers for similar boats over the years, I’m in the ball park.  But that’s a longs ways to the 40-42 mph his gps claims to be getting.  My wot during survey was 42.
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  • GrahamuGrahamu Member Posts: 921 ✭✭✭
    I have to admit I found those speed numbers very high. I would think my 342 is similar in size and weight. My speed is showing on my small Garmin Chart Plotter and my tablet running Navionics.
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  • davidbrooksdavidbrooks Member Posts: 1,432 ✭✭✭✭
    2003 342 with Merc 350 MPI and Bravo 3s.  I couldn't hit 48mph if i was going downhill and had a good strong tailwind. I used to have 3 blade 24p props and switched them out for Hill Marine 4 blade 22P.  I used to be able to get to 40 mph...44 in perfect conditions. Now i get up to 38mph max.  So i did lose some top end speed.  I also have not gone above 4400 wot.  What seems to be a comfortable speed for me is right at 28-30mph and that is 3200-3300 rpms.  As far as coming off plane.  If i go below 22mph i have to use tabs. Seems like 22-24mph is the minimum for staying on plane without tabs.
    It's 5 O'Clock Somewhere!
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  • CnCCnC Member Posts: 142 ✭✭
    Well maybe its time for a new Raymarine then? I'm just throwing the numbers out that come up on the unit trying to get a good starting point. My "wants list" at this present point is to simply get on plane a bit quicker and not over rev the engines to the degree of sending a rod out the side of one the blocks. If that number is 22-24mph then I'm happy with that. Again top end speed is of little concern. When you guys say you have to use your tabs do you do anything with the outdrive trims before utilizing them?
     Also one question off topic a bit we're heading to an island later this evening so what are some suggestions for increasing battery life over a couple day span. Can you shut down one of the fridges (say the one up in the cockpit?) and only use the one? Run the engines for a bit in the evening to charge the batteries and for how long? I plan to pick up a solar panel  blanket that we can easily store when on shore power but haven't purchased yet. Any advice would be appreciated
    Thanks in Advance
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