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Old 09-01-2015, 14:01   #1
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Dinghy/Outboard performance???

Last year I replaced my dead 2.4m Quicksilver AirDeck (inflatable keel) with a 2.4m Honwave (air V-floor) and found I had a massive drop in speed with my Tohatsu 3.5hp 2 stroke.

With the Quicksilver I could almost get it to planning speed one up although it would suffer cavitation and the speed will drop off. With the Honwave it does not come close to the same sort of speed. I'm not sure if it's just a problem with the Honwave design or perhaps the winter service of the Tohatsu lost it power???

There is temptation to get a new 6hp OB (Max recommended for the Honwave)

I'm just curious to know what inflatable/rib & motor combos people have and how you find the performance and are you happy with the combo?
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Old 09-01-2015, 14:29   #2
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Re: Dinghy/Outboard performance???

That outboard is too small to reliably plane a dinghy of that size. It's very marginal. So presumably it only just planed your old dinghy, and now it won't quite.

6hp sounds good to me!

I had a 6hp on my 8ft 6" Achilles wood floor / air keel, and that was a bit marginal. Changed the carb and exhaust which boosts power to 8hp. Planed reliably then, but very wet. Now have a Zodiac Compact RIB 9ft 6, with the 8hp, works beautifully.
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Old 09-01-2015, 14:33   #3
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Re: Dinghy/Outboard performance???

No doubt extra horsepower will help. Hull shape has a big effect on planing ability. It's the angle at the stern that makes the difference (it's called "deadrise"). Inflatable's soft hulls if not taut can also act like a suction cup on the water, increasing drag and further adding to the load. With a marginal engine like the 3.5 it won't take much to stop it "getting over the hump". The shorter the dinghy, the harder it is for it to get on the plane as well. A stumpy 2.4 is a pain in this regard. Have you tried an extension tiller (a.k.a. piece of 40mm PVC pipe) and tried to sit in the centre? This can help performance enormously. I use a 5hp on a 10 and 11 foot hard dinghy and it will plane with me (100kg+) and a little bit of gear onboard very easily on both if I use my tiller extension and sit on the centre thwart. My 3.3 on the same boats doesn't go close to planing although I can get my 2.9m inflatable RIB to plane with it - just - if I sit in the centre.
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Old 09-01-2015, 14:36   #4
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Re: Dinghy/Outboard performance???

Really happy with our highfield ultralight 310 (45kg) and Johnson 2 stroke 9.9 (36 kg)
Planes easily with 3 adults, not so easily but sometimes with 4 adults. Planing speeds around 17K. Easy to drag up on the beach alone. Actually I just figured out the easy way after struggling with pulling it up for years. Just walk it up sideways, drag the ass up a meter, then the bow, then the ass again till it's high and dry. Much easier than pulling it straight up...
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Old 09-01-2015, 15:38   #5
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Re: Dinghy/Outboard performance???

Quote:
Originally Posted by Reefmagnet View Post
Have you tried an extension tiller (a.k.a. piece of 40mm PVC pipe) and tried to sit in the centre? This can help performance enormously.
The throttle is on the motor housing and I can lean forward steering by moving weight left & right. On the old quicksilver this was how I could get the speed up, but not on the Honwave. I also tried adjusting the angle of the motor to improve trim without any luck
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Old 09-01-2015, 16:45   #6
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Re: Dinghy/Outboard performance???

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Originally Posted by hoppy View Post
The throttle is on the motor housing and I can lean forward steering by moving weight left & right. On the old quicksilver this was how I could get the speed up, but not on the Honwave. I also tried adjusting the angle of the motor to improve trim without any luck
I used to tighten the steering friction bolt and tap the motor until the boat ran in roughly a straight line and do the same weight shift steering thang on my old Avon Redcrest sans hard floor and that pool toy used to actually start scooting along once it got some revs up in calm water. Had to give the tiller an occasional tap to correct for torque steer lol. On the RIB, I just threw the throttle full on and moved forwards. Things don't happen that fast enough for it to be a problem. Moving weight back aft slows the boat rapidly as it forces it off the plane even at full throttle when powered by one of these little motors.
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Old 09-01-2015, 16:47   #7
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Re: Dinghy/Outboard performance???

Best combo I have ever seen was my previous rig:
310 Mercury Airdeck with a 2009 Yamaha 4 HP, 4-stroke.
With a 220 Lbs Norwegian Stud onboard I could do 10.9 knots.
Leaning way forward and with a tiller extension it would plane on flat water.
Any waves would slow down the magic, so would another person onboard, but still, 10,9 from 4 HP was pretty spectacular.
(Had a previous 4 HP Evinrude 2-stroke on the same dink and it would only do 7 knots plowing the water, not planning. Higher RPM and screaming, but the 1 cylinder Yahama had much more torque. Or HP, but they were both sold as and rated at 4 HP)
Go figure....
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