Dink won't plane

[rastamon]

Hey all,
I recently bought a smaller dink (10') and was going to use an old Honda 8hp 4cycle long shaft I had stored. I used it as a kicker on previous boat. The dink is old RIB. Is the fact the motor is 23" long shaft a contributing factor? Suggestions?


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[paulajayne]

Trim? Maybe move your weight forward when at full throttle to bring it onto plane?.


8HP is a smallish engine as well.

[Stu Jackson]

NEI - not enough information .

How heavy are you and/or did you have another person or more on the dinghy?

How much fuel on the dinghy? 6 gallon, 3 gallon?

OLD RIB: What hull material?

What max HP is the dinghy rated for?

Do you have a tiller extender?

Things like that.

[rastamon]

I'm 165lbs, let's just say Admiral weighs less🐬 I've tried both ways. Alone and not. Old Boat US dink fiberglass RIB weighs 145lbs. Rather for 10hp. Recommended for 8hp. Carry 3 gal. Fuel ahead of seat no tiller extension.


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[model 10]

You need at least a 10hp for that boat. An 8hp will /should plane a 9' with 1 person.

[a64pilot]

Long shaft is a whole lot more drag, and it may well be propped completely "wrong"
Is the motor revving out, as in motor sounds like it's running fast, just the dink isn't going all that fast? Or is the motor lugging down and won't rev up?
I have no experience with a long shaft motor on a small boat, gut feeling is it will never be "right", but may work.

[sailjumanji]

Hard to believe you are having problem even alone. I have a 10.5 ft Avon lite rib with 8 up two stroke and can plane two adults around 400 lbs at 23 mph wot. It takes leaning weight toward front on takeoff. With single 200 lb person it jumps on plane immediately. Maybe your issue is the extra motor weight and length. Don't know.

[Cheechako]

Sounds like you are marginal on HP. The long shaft an issue also. That's a heavy dink .... adding to the problem. The Honda 4 stroke is heavy too. It all adds up.

[S/V Illusion]

Originally Posted by rastamon

Old Boat US dink fiberglass RIB weighs 145lbs.

I think you just answered your own question.

[a64pilot]

If it was used as a kicker motor for a much larger boat, wouldn't it probably have a very low pitch prop?

[keepondancin]

Might try something like Doelfins to get some lift, but 8hp is a bit light for a 10' RIB, plus it might be a high thrust prop.

[Vasco]

It's the long shaft. No way you'll get it to plane with that shaft.

[Jim Cate]

Have you tried changing the engine tilt angle? With the long shaft, the thrust is well below the WL of the dink, and thus the angle has a larger effect on the attitude of the hull under power.

And fwiw, we used to have a 13 foot soft bottom Zodiac (an old Mk 2) with a long shaft 15 and it planed easily with two up and a load of boat stuff on board.

Jim

[rastamon]

Hey thanks for all the advice.
It is a "high thrust" engine and is revving up ok. I have adjusted the angles with same results. And figured the extra long shaft might be the problem. If ya see a "for sale or trade" posting, it's probably me!!!
Fair winds ⛵️


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[Pete7]

Sorry to say this but you have completely the wrong engine. Mercury and Mariner have a sailmate engine with a high trust prop and lower gearing designed to move a small motorboat or yacht. I suspect you have the Honda equivalent.

Measure the transom from top to bottom of the V. It is probably 15-16" so you need a short shaft engine. 21-22" require standard shaft length. Ditch the Honda and buy one the right shaft length. then mount so the ventilation plate is 1" above the bottom of the V as a start point. Suggest a 2 stoke engine as weight seems a bit of a problem. If you can find a Merc Seapro engine they have extra stainless steel parts inside which will help, something like the old X10 engine.

Pete