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Old 19-06-2011, 21:29   #1
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5hp Tohatsu, 9' Dinghy - Plane?

We have a 5hp Tohatsu 2 stroke, prop 7.8 x 8, hardly used, on a 9' De Haviland aluminium dinghy.

Together the dinghy and outboard would weigh 50 odd kg, the total "ask" (dinghy, outboard, "crew", supplies) is about 200kg.

I haven't run the engine flat out (less than 100 hours - still running in) but I get the sense that its never going to get the dinghy onto the plane.

But from other threads it looks just about possible.

So, is it possible to get a 9' dinghy with 200kg all up weight onto the plane with a 5hp outboard, and if so are there any "tricks" - different pitch on prop, cavitation plate, changing engine angle, redistribute weight in boat, loose a few kilos, fiddle with carburetor - that can help?
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Old 19-06-2011, 21:45   #2
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Boracay
No magic tricks you probably need at least 15hp to make a tinny with gear plane
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Old 19-06-2011, 21:49   #3
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Some dinks with 9.9's can plane.
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Old 19-06-2011, 22:06   #4
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Planning my 10,3' air-floor dink with a 4 HP Yamaha.
Getting 11 knots in calm waters.
The dink weighs 103 lbs, motor is 48 lbs and the skipper is uh, 230 lbs, then fuel cans, light gear, etc for a total of 178 KGs or 391 lbs.

The secret is a tiller extension and lean way forward. Also took some experimenting with the motor angle, pressure in the keel, etc.

Forget it with 2 persons onboard, but with just me it flies across the water and I am quite impressed with the 2009 4-stroke Yamaha 4 HP.

Previus motor, 4 HP, 2 stoke Evinrude could only push at 7.5 knots regardless how much I tweaked it and leaned forward.
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Old 19-06-2011, 22:27   #5
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

I have a 9' achillies with the very same motor you have with myself it planes off fine Have not tried it yet with two people but feel with weight forward it plane
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Old 19-06-2011, 22:37   #6
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

I once had about the same setup but with a nissan 5. I could get it to plane (by 0.00001mm) but I had to stand in the middle of the boat and steer by leaning the skiff. It was fun. I had no tiller extension, I was 30 and brave and surfing every day.
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Old 20-06-2011, 03:09   #7
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Quote:
Originally Posted by CSY Man View Post
The secret is a tiller extension and lean way forward. Also took some experimenting with the motor angle, pressure in the keel, etc.
x4 on this advice.
Need calmer water; can plane on 4hp with weight forward.

Seen it done with one adult, one child, and towing a plastic shark!
Darn that hard drive crash, or I could post the piccie.
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Old 20-06-2011, 05:13   #8
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Both a flatter pitch prop and a Doel-Fin will help it plane. Doubt if it will plane with more than one person though.
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Old 20-06-2011, 05:45   #9
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

We have a 10 ft wooden floor archilles with a 5 hp Nissan(2 stroke) and it will plane with me at 200lbs and wife at 130 lbs. Once up on plane it will stay there, but must move weight forward and have fairly flat water to initially plane with 2 people. I did change out the prop when I first bought the motor back in 1993, but can't remember if I increased or decreased the pitch from standard.
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Old 23-06-2011, 04:33   #10
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

Photographic proof of concept: hopefully the photo will upload!

Planing on four horsepower. Weight forward.

One adult, one child, plus plastic dolphin (answers to name of "Sharkie").

Thank god for file recovery software!
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Old 23-06-2011, 06:47   #11
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Re: 5hp Tohatsu, 9' Dinghy - Plane?

A 4 stroke has a great deal more torque than a 2 stroke for same horsepower rating. Mine with a 10 horse (2 stroke) Johnson 9' RIB planes easily. My previous motor I could plane by moving weight forward, and accelerate until at max, then reduce throttle for 2 secs until sternwave catches up and lifts transom, then full throttle as waves moves under boat to surf down stern wave. It only worked in right conditions.
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