how fast should an inflatable dinghy go..

[kashurst]

Just got a new 2.3m dinghy with inflatable v floor. put my old 4 hp mariner on it and it does @ 6 knots (estimate) I can't get it to plane properly as the motor doesn't seem to have quite enough power. max rating for the dinghy is 5hp - would that be enough to get over the hump?

 

[hlb]

Got a 2.6 Avon and 4hp, goes like hell with one in. How much do you weigh???

 

[VicS]

Your dinghy manufacturer should be able supply info on the expected speeds for various engine powers, with a specified number of persons on board. At least Avon do. Try the website.

You do not say how old your "old Mariner" is but the methods of power rating for outboards was changed in the early 1980s from the crankshaft power to the prop shaft power. An old 4 hp would probably only come out at about 3 hp on the new scale.

Propeller pitch is something to also consider. A coarser prop may get you going faster but only if there is sufficient power available.

 

[Nick_H]

I doubt you were doing 6 kts if you weren't planing. V floors need a bit more power to plane than a flat floor. Having said that, I just about got a v floor 2.4m on the plane with a 3.3 hp 2 stroke, but the tender is superlight (20kgs), and I had to lean right over the front, so I couldn't reach the outboard to steer. Even on the plane though, it probably wasn't doing more than 8-10 kts.

 

[hlb]

Sit further forwards.

 

[Rhosneigr Gaz]

Boat Mart did a test a couple of monthas back with about a dozen inflateables, slatted and airdecks.

they got them all to plane with 2hp or 4 hp if i remember correctly?

Now thats not to say you aren't 20 Stone and sat on the transom!!!

I would expect a 4hp to get most tenders up an flying!

 

[kashurst]

thanks for the replies gentlemen, just for your info I am @ 12 1/2 stone and the engine is 12 years old. I now strongly suspect its well past its best by date. Would a modern 5Hp engine do the business ????

 

[hlb]

My Mariner is at least 20 years old.

It wont plane until you sit forwards till you can hardly reach the throttle.

 

[GrowingLad]

Would a modern 5Hp engine do the business ????

Yep...

I've got a 2.3m with a slatted floor and a 5HP 2 stroke Mariner...it goes like a bat out of hell with just me on it. Two people and it won't plane but with just one...real good grin factor..especially if there's a few waves.

When we go away for a break, I take my inflatable and outboard so I can get further out to some good snorkelling spots....Found myself a nice fold away anchor, chain and 40 meters of rope some poor soul must have dropped....Nearly busted a lung diving down for it but it's come in handy.

 

[hlb]

Yep...

I've got a 2.3m with a slatted floor and a 5HP 2 stroke Mariner...it goes like a bat out of hell with just me on it. Two people and it won't plane but with just one...real good grin factor..especially if there's a few waves.

When we go away for a break, I take my inflatable and outboard so I can get further out to some good snorkelling spots....Found myself a nice fold away anchor, chain and 40 meters of rope some poor soul must have dropped....Nearly busted a lung diving down for it but it's come in handy.

Sounds like theres not much better effect with 5 hp than 4hp, my 4hp will go fast enough to frighten.

 

[Kawasaki]

Sounds like theres not much better effect with 5 hp than 4hp, my 4hp will go fast enough to frighten.

Thats cos when I 'serviced' it
I put a new Flux Capacitor in in it , innit.

Plus I think yer need to go on a Course fer Ding drivin

The new Liverpool based 'R ay L' one I've just started

'R ay La, ow der work a ding La'

 

[GrowingLad]

Sounds like theres not much better effect with 5 hp than 4hp, my 4hp will go fast enough to frighten.

Oh this sounds like a challenge

Before you know it we'll be up to this lark

http://www.youtube.com/watch?v=2rSrDq08vbQ

 

[[2068]]

2.40m Slatted floor Quicksilver.
5hp Merc 2-stroke.
17st skippero) + skinny 5yr old = planing without issues.

 

[epervier]

2.7m rib 107 kilo fatty at the tiller of a 15 horse 2 stoke it wants to go vertical, put the fat past the seat the thing goes over the hump and scares the livin' **** out of me, it's far too twitchy, on the edge of down right dangerous. I think I'll go back to the 4 horse yam.

Far safer with two, slows it down to a more hand-able turn of speed

 

[ash12]

My old valiant d-300 (3m) rib would get on the plane with ease with an old yam 4hp 2 stroke on the back.

 

[Andrew_Fanner]

My old Avon 270 riblet would do >22 knots one up with 10HP on the back. Marine equivalent of go karting. Never dared open the throttle to the max. The "replacement" airdeck is lighter but twitchier. Planes nicely with 3 kids and I on board though.

 

[kashurst]

I think my old 4hp mariner may be a liitle worn - anyone know a website where I can get a manual from so I can inspect the insides to see if its worth fixing ???

 

[mitchc]

Sit further forwards.

I agree with HLB, try sitting further forward. Make sure it's trimmed correctly too (is there a pin you can adjust?)

My 3.2m airdeck Honda is good for nearly 20knts with a 8 hp 2 stroke yam. Don't even ask what it's like with a 15hp 2 stroke fitted!!!

 

[asteven221]

My Lodestar 2.6 with a Yam 4hp 4 stroke will plane, but it does need a bot of persuasion to get over the hump. Once over it flies and I weigh a tonne.

 

[Nick_H]

That's a good point on the outboard trim. Get a straight edge and hold it along the keel, then align the cavitation plate parallel with it by removing the pin and sticking it in the appropriate set of holes in the mounting bracket. The cavitation plate should be 0-50mm lower, but I prefer it much nearer 0 than 50. You could then try it toe'd in (is that the right expression?) one setting, as that will help it plane.

I'm surprised at so many people saying their tender pops up on the plane and flies with a 4 hp outboard, i'd have thought it would be pretty borderline, and need lots of shifting your body weight around.