Planing help with 8'10 inflatable - new to this!

[lancew]

Hello!

I recently got my first (engine-powered) boat - an 8'10 inflatable. Has a soft floor with a few wooden slats fitted to it for rigidity. It's powered by a 4HP Tohatsu 4-Stroke outboard.

I can get it up on plane well enough with just myself and some gear (gas can, small cargo box, a couple of lifejackets and a seat pad) however cannot keep it on plane. It seems that once on plane for 30 seconds - 1 minute, the engine will suddenly stop spinning the prop and rev up really high. More than once it has almost thrown me out of the boat/off balance. Once the small wake behind the boat hits the engine, the prop will kick back in and I'll accelerate again, but no longer planing (since the speed died so quickly/drastically).

I'm assuming this is due to the boat/engine cavitating, but not sure why the engine would stop the prop and rev up. I'm assuming that the prop stops also, based on the behavior of the boat - I have no way to look. If I shift my weight to the back, the prop will engage again. I cannot get it on plane while sitting at the back to begin with.

Would this be due to the engine not having enough water to suck in to cool itself, so as a safety it throws it in neutral/stops the prop? If so, what would be the solution for this - lowering the motor (also known as cutting the transom)?

This happens on rough and calm waters (though reaching plane on the ocean/with waves is more difficult).

Help please and thanks!

 

[Guest]

Re: Planing help with 8'10 inflatable - new to this!

Hello!

I recently got my first (engine-powered) boat - an 8'10 inflatable. Has a soft floor with a few wooden slats fitted to it for rigidity. It's powered by a 4HP Tohatsu 4-Stroke outboard.

I can get it up on plane well enough with just myself and some gear (gas can, small cargo box, a couple of lifejackets and a seat pad) however cannot keep it on plane. It seems that once on plane for 30 seconds - 1 minute, the engine will suddenly stop spinning the prop and rev up really high. More than once it has almost thrown me out of the boat/off balance. Once the small wake behind the boat hits the engine, the prop will kick back in and I'll accelerate again, but no longer planing (since the speed died so quickly/drastically).

I'm assuming this is due to the boat/engine cavitating, but not sure why the engine would stop the prop and rev up. I'm assuming that the prop stops also, based on the behavior of the boat - I have no way to look. If I shift my weight to the back, the prop will engage again. I cannot get it on plane while sitting at the back to begin with.

Would this be due to the engine not having enough water to suck in to cool itself, so as a safety it throws it in neutral/stops the prop? If so, what would be the solution for this - lowering the motor (also known as cutting the transom)?

This happens on rough and calm waters (though reaching plane on the ocean/with waves is more difficult).

Help please and thanks!

sounds more of a engine issue, I would post this on the Tohatsu thread.

 

[lancew]

Re: Planing help with 8'10 inflatable - new to this!

sounds more of a engine issue, I would post this on the Tohatsu thread.

Will do - thank you!

 

[fbpooler]

Re: Planing help with 8'10 inflatable - new to this!

Most slat floor boats are not planing craft.

 

[Sinistre1]

Re: Planing help with 8'10 inflatable - new to this!

That the boat planes at all is impressive. Not really designed to do so if it has a slat floor. It will not hold its shape under power and the changing shape presents different loads on the boat and motor forcing it off plane. I imagine it might stay on plane (with no directional stability) if the slats were replaced with a solid floor.. but then that is a different boat altogether.

 

[Sea Rider]

Re: Planing help with 8'10 inflatable - new to this!

Yep, the slatted floors are the worst of all inflatable floor models, are intended as tenders at fast displacement speeds, Installing a wooden floor will not be of much help as slatted floor sibs lacks a inflatable lower keel. Try pumping up that sib to it's max recommended working pressure with gauge, remove all gear, try it solo, see what happens. Is it a used or new engine, if used, could be experimenting a spun hub assuming engine sits on transom at a correct proper height.

Happy Boating

 

[lancew]

Re: Planing help with 8'10 inflatable - new to this!

Thanks for all the replies!

Engine is new, I highly doubt it's a hub issue. I did measure and the cav plate is about 2.7" below the bottom of transom. I'm making a small jack plate to compensate.

I'm sad to hear that it could be the slat floor. I'm contemplating a wooden/plywood floor..

 

[Sea Rider]

Re: Planing help with 8'10 inflatable - new to this!

Are you experimenting water splashes over transom at wot as to experiment excessive water drag on tail and engine power loss ? If not, raising engine won't do much. If contemplating a wooden/playwood floor to be placed on top of slatted floor will just add rigidity to deck, that sib doesn't count with an inflatable keel under hull to help cutting water drag under, so near useless. Sib has too much hull drag and size doesn't help at all.

You could probably benefit upgrading that 4 HP into a 5, as both are same size and same weight, will have slight more engine punch than with 4 HP and probably better to maintain plane. BTW, what's your weight ?

Happy Boating