Dinghy motor suggestions

craigswardmtb

I have a 9' inflatable floor dinghy and currently use a 3.5hp Tohatsu 4 stroke.  It works fine for getting us from boat to beach but it is a dog when it comes to speed with more than a person in it.  I can get it on plane with just me in the boat (175lbs) but anything else it won't.  And when on plane it seems like the prop struggles to grab once i get up to full speed and then I have to throttle down and then get back on plane only to have it happen again.  I'm curious what causes this?  Could it be the cheap plastic/resin prop that comes standard on these motors?  I thought perhaps there was flex at higher speeds/rpms.  Or maybe its the short shaft length?

I'm not looking for miracles as I know it would require getting a different motor but just suggestions on what might fix my challenges if anything.  First I would like to fix the planing issues when at full speed.  Second I would like to have a bit more thrust to get this thing moving when it has more than just me in it.

It comes standard with a 7.4" x 7 pitch 3 blade plastic resin prop.  I'm curious if switching to the moderate duty resin prop they offer would remedy my issues (5.7 pitch prop).  THey also offer an aluminum one which is a 6 pitch prop.

Let me know what you think.

andyd

Since the plastic props are relatively cheap you could try the 5.7 and keep the old one as a spare. I'd talk to a shop that specializes in outboards. Honesty, if you are looking for a higher performance planing inflatable you might want to look at RIBs and getting a lot more horsepower.

Me, I'm content to put around at 5 knots because 90% of my dinghy use is within speed limited harbors.

Andy

skidrow

What kind of dinghy do you have?

I have had the same problem.

Thought it was the prop etc...

Is it a RIB or a vinyl air bottom with a inserted plastic/air/or wood floor?

If it isn't a RIB bottom, the boat bottom will flex with the additional weight

just enough to throw the motor out of plane. This will cause the motor to

cavitate. You will then slow down to drop the revs and again try to accelerate on plane and have it happen again....RIB's are hard bottom and don't flex.

craigswardmtb

That makes sense. It's a Bombard max 3+ with inflatable bottom. 

JC290

Prop change would help how much is another story

skidrow

Don't waste your money on a new prop..been there..didn't do anything..its the bottom flexing...best thing is a RIB.

Black_Diamond

Yup. RIB makes a huge difference. Go for hypalon if you can afford it. I went with an AB dingy with an AL hull, weighs less than my old 270 airdeck and is 9.5' long with another foot of beam. It flies with a 9.9 2 stroke. 

JoeStang

You can also try a small hydrofoil. I was getting terrible porpoising, and I adjusted the trim one notch from all the way "down" and installed a Stingray Jr hydrofoil. It planes and rides perfectly level now.