Dinghy engine power

[prv]

Yet another dinghy thread...

I currently have a very tidy Suzuki 2.2hp 2-stroke outboard for the tender. It's reliable and I can lift it on and off the boat with one hand, but obviously it provides displacement speeds only.

I'm wondering if it would be feasible (re budget, and to some extent weight) to upgrade to something that will allow the new dinghy to plane.

How many horsepower would be needed to get, say, a 2.5m air-floor inflatable to plane with one fat bloke on board? Any chance of planing two or three up?

I tend to prefer 2-stroke, though I'm not ruling out 4, and would wait for a good second-hand engine to come up and then give it a thorough clean and service.

Thanks,

Pete

 

[MikeBz]

I had a DT2.2 which would just get my 2.7m Bombard Air Deck onto the plane with me (13st) on board. I now have a Honda 2.3 which doesn't even come close to doing so - I guess Suzuki horses are somewhat bigger than Honda ones!

 

[Davy_S]

My old AX2 air deck would plane,11knots with a 4hp Suzuki 2t, it could have done with a tiller extension, it was a little hairy!

 

[Steve_N]

I had a DT2.2 which would just get my 2.7m Bombard Air Deck onto the plane with me (13st) on board. I now have a Honda 2.3 which doesn't even come close to doing so - I guess Suzuki horses are somewhat bigger than Honda ones!

Suzuki horses are smaller then Mercury ones though!
2.7m airdeck, just me on board, easily planes with a Mercury 2.2 two stroke.
Suzuki 2.5 four stroke - no chance..

 

[prv]

My old AX2 air deck would plane,11knots with a 4hp Suzuki 2t, it could have done with a tiller extension, it was a little hairy!

Thanks - this is looking promising, as those figures are less than I imagined (I've never had or used a tender that could plane, always just the 2hp version).

I do wonder how much difference weight makes, though. I weigh 120kg, or just under 19 stone in old money, so Mike's Suzuki ain't gonna do the trick for me

Pete

 

[prv]

Suzuki horses are smaller then Mercury ones though!
2.7m airdeck, just me on board, easily planes with a Mercury 2.2 two stroke.
Suzuki 2.5 four stroke - no chance..

It's looking like the 4-stroke horses are smaller than the 2-stroke ones, rather than anything to do with the label. Assuming Mike's Honda 2.3 is a 4-stroke, which seems likely.

Pete

 

[MikeBz]

Yes, it is a BF2.3 in excellent, serviced condition. The DT2.2 was an old one that I bought for £130. I gave up on it because the coolant channels in the head continually blocked despite flushing after every use - shame because apart from that it had the potential to be a really good little engine. Now in bits in my garage, waiting for me to find the time to fix it up & sell it.

 

[rob2]

I'd suggest the Tohatsu 3.5 (or <ariner/Mercury 3.3) 2 strokes for light weight and a bit of oomph, but you won't plane with two mates aboard unless you go to around 5hp and they're getting heavy to manhandle up to the rail from the dink. Worse still is trying to lower it in a controlled fashion back to the poor unfortunate sitting belneath you with upraised arms. We used to sail a Thompson T24 which had a transom door so we could just slide the 5hp Yamaha out to the dinghy, but I wouldn't want to use that one on my Weston with 39" freeboard at the stern.

Rob.

 

[TQA]

I do see the odd dink planing with less but basically you want an 8 hp for one biggish person and 15 hp for 2 -3 for reliable planing. Anything less will be marginal and may require a downwind run to get her up on the plane.

That is what is in general use out in the Carib.

 

[Davy_S]

I do wonder how much difference weight makes, though. I weigh 120kg, or just under 19 stone in old money, so Mike's Suzuki ain't gonna do the trick for me

I think weight makes a great difference! I am a very athletic 12 stone Also, a lot more grunt with a 2T, than a 4.

 

[Storyline]

An air deck (or solid floor) is essential - I know this as ours has a small leak so for the first few hours will plane easily but as it starts to get a bit soft everything changes. Have you considered a small crane to help with the o/b,? The one we have is one of the best bits of kit on the boat. Not cheap as it is a US import (Nova Lift) but you can probably get cheaper ones or have one fabricated.
As regards weight, as others have said it makes a huge difference when you are on the margin with these small engines. Used to have a twin cylinder 4hp Johnson o/b and at my heaviest (13.5) stone it would struggle to plane with a Avon Rover 2.8. After the 'new me' transformation I weighed 10 stone and it would yplane easily. Now have a Tohatsu 5hp 2st and it will easily plane both my wife and I.

Serious about the crane though - many, many times we have had people come over to our boat in an anchorage to ask about it when they see how easy & safe it is to lower the o/b onto the dinghy.
View attachment 44367

 

[reeac]

I designed and had hade in S.S. A mini davit nearly 10 years ago. Had it featured in PBO at the time. The emphasis is on compact unobtrusiveness but it can carry my weight of 75 Kg. Its attached to the pushpit. Have a pic. Somewhere if anyone is interested.

 

[landlockedpirate]

Nautorius has a 2.5m Quicksilver Air Floor out in Gib with a Yamaha 4hp 2 stroke. It will just plane with a 'big boned' helm on board if you use a tiller extension and hang over the bow.

You can get the same engine but in 5hp, that would work better.

To plane with 3 up ? I think you are going to need 15hp.

 

[Daydream believer]

I do not think that it is all horse power but torque & revs etc
My Mariner will not make my dinghy go as fast as I can row it, but my Seagull 40+ ( Don't you just love em!!!) will go significantly faster with a lower horsepower
I prefer the Seagull every time but the daughter rebels when asked to carry it

 

[prv]

Nautorius has a 2.5m Quicksilver Air Floor out in Gib with a Yamaha 4hp 2 stroke. It will just plane with a 'big boned' helm on board if you use a tiller extension and hang over the bow.

You can get the same engine but in 5hp, that would work better.

To plane with 3 up ? I think you are going to need 15hp.

Thanks - I'm happy to accept that planing three-up might not be feasible. But it would be nice to travel quickly when on my own.

Pete

 

[Greenheart]

I think weight makes a great difference! I am a very athletic 12 stone

I'm a terrible lardy slack-arsed 12 stone, so I expect I'd need a bigger o/b to reach the same speed.

 

[jerrytug]

Tohatsu 3.5 2T gets both Yam 2.2m and Bombard AX2 up on the plane with me and a heavy rucksack, but you need to extend the tiller, to move your weight to adjust fore and aft trim.
That said it's planing, but it's still not so very fast. However I am right on the plated motor weight and power limit.
My last AX2, I ripped the transom off the tubes with the same engine, that slows you down a bit..

 

[Spyro]

Seago 260 slatted floor will plane easily with my johnson 3.5 and my 14 stone. Does 12 or 13 knots. It wont plane with 2 on board.

 

[stevebrassett]

I'm a terrible lardy slack-arsed 12 stone, so I expect I'd need a bigger o/b to reach the same speed.

If you can keep your arse out of the water, you might make it.