Which outboard?

[PaulJS]

I've just bought a new 2.6m slatted bottom inflatable dinghy, I haven't actually seen it yet as I'm at work, but from the figures given I'm assuming it's got quite big tubes as its rated capacity is 450 kg.
Unfortunately, the website blurb doesn't give a maximum Hp/weight for the outboard, so what size engine do you think would be suitable for pottering around a fairly well sheltered estuary which has occasional currents of up to maybe 4 knots when they open the hydro power sluices one mile upstream.
Also any recommendations?

Thanks,

Paul

 

[Stu Jackson]

Those slatted bottoms don't take and/or can't handle much. I'd be thinking 2 hp. Try the vendor's website for recommendations for maximum HP suggestions.

 

[sailorman]

we have a Tohatsu 3.3 2T on a Zodiac 2.3m works fine

 

[PaulJS]

Those slatted bottoms don't take and/or can't handle much. I'd be thinking 2 hp. Try the vendor's website for recommendations for maximum HP suggestions.

Thanks Stu. Would 2 Hp be able to push a 30+ kilo boat against 3-4 knots of current? I was assuming more in the realm of 3.5 to 5 Hp as one of the chandlery websites states a 8Hp maximum for a similar, but smaller carrying capacity 2.6m, rigid transom, slatted bottom dinghy.
That's the real reason for starting this thread, I'd like to buy the lightest (And cheapest!) engine that will enable me to potter along at more than walking pace, and as I mentioned, the local tide and current can be quite strong.

 

[Twister_Ken]

Usual recommend for a 2.6 is up to 4 ponies. Beware, though, that a 4 might weigh somewhere in the region of 25 kg. OK if you're happy lifting that around. A 3.5hp can be had for 17kg.

I used a 2hp on the Hamble where the tide runs pretty quick sometimes, but by sticking to the shallows it's possible to make good progress.

 

[PaulJS]

Usual recommend for a 2.6 is up to 4 ponies. Beware, though, that a 4 might weigh somewhere in the region of 25 kg. OK if you're happy lifting that around. A 3.5hp can be had for 17kg.

Thanks Ken. One of the cheaper Chinese makers claims 22kg for both it's 4 and 5 Hp motors. I thought that was reasonable compared to the old 5 or 6 Hp two-stroke I have already, but unfortunately I'm 3000 miles from it and can't even remember what make it is - I suspect that it's an Evinrude/Johnson and if it's a "Sea Horse" which looks quite familiar, it's claimed weight is actually only 21.5 kg! I always thought it was a lot heavier than that - must be getting old .

I think the 3.5 Hp at 17kg is favourite at the moment, what sort of speed does anyone think that would push the dinghy at?

 

[seumask]

Go for a 3.3, 3.5 2T Merc, Mariner, Tohatsu, all the same basic and relly good engine. dont be afraid of a 2nd hand one, they are light around 13 Kg and have enough power. Press on the cheap Chinese ones is not always very positive and they are on the whole less power full than the posher well know makes.

 

[VicS]

I've just bought a new 2.6m slatted bottom inflatable dinghy, I haven't actually seen it yet as I'm at work, but from the figures given I'm assuming it's got quite big tubes as its rated capacity is 450 kg.
Unfortunately, the website blurb doesn't give a maximum Hp/weight for the outboard, so what size engine do you think would be suitable for pottering around a fairly well sheltered estuary which has occasional currents of up to maybe 4 knots when they open the hydro power sluices one mile upstream.
Also any recommendations?

Thanks,

Paul

You dont say if its around tail or solid transom dinghy

Assuming a solid transom
Looking at an old Avon catalogue ... rather than pulling figures out of the air
I would estimate up to around 5 or 6 hp would be fine.
450kg capacity is quite high so outboard weight should not be a problem.

Extrapolating the available info a bit but I'd expect something like 7 mph with a 6 hp and two persons but probably no more than about 5 mph, if that, with a 3 hp

Nothing like these figures for a round tail though .. more like 3 hp max for engine size

You should be able to find all this info for your dinghy though.

Standard/ short shaft!

 

[rotrax]

I've just bought a new 2.6m slatted bottom inflatable dinghy, I haven't actually seen it yet as I'm at work, but from the figures given I'm assuming it's got quite big tubes as its rated capacity is 450 kg.
Unfortunately, the website blurb doesn't give a maximum Hp/weight for the outboard, so what size engine do you think would be suitable for pottering around a fairly well sheltered estuary which has occasional currents of up to maybe 4 knots when they open the hydro power sluices one mile upstream.
Also any recommendations?

Thanks,

Paul

Hi, I have had-and am having-superb service from the Johnson 3.3 and 3.5 hp two strokes.They are light,easy to start, very reliable and punchy. Last year my 3.5 did not start. I had to pull the cord again.

 

[PaulJS]

Thanks to everyone for the advice, sorry I didn't make it clear that it's a hard transom dinghy in the OP.
I've got no doubt that a max Hp/weight will be specified on the dinghy name plate, but as I'm 2 weeks and 3000+ miles from unwrapping it I was hoping that the accumulative wisdom of the forum might help me to decide whether or not to stick with my present 5 or 6 Hp two stroke, which always seemed damned heavy, or if I would have good reason to be able to convince "the boss" that a nice, shiny, reliable new four stroke would be a justifiable expense!
I guess that the wisest course is to wait until I get home, check the dinghy, and confirm the weight of my present motor!

 

[JClarkes]

I have a Yamaha 2hp 2stroke petrol outboard. Very light at 25lbs. An older outboard but very reliable and easy to maintain. My Granda used to be a Yamaha dealer so I would be cuffed around the lugs if I used anything else

 

[webcraft]

. .. if I would have good reason to be able to convince "the boss" that a nice, shiny, reliable new four stroke would be a justifiable expense!

4-strokes are heavier per horsepower and, in the experience of most of the people I know, a lot less reliable. I would stick with a 2-stroke.

- W

 

[PaulJS]

Thanks again.
I doubt whether a 2 Hp would be powerful enough considering the weight of the boat and the tide and current in my local estuary.
I know that a two stroke theoretically gives more power per kg, but on the flip side modern four strokes are much more fuel efficient and nearly as powerful per kg, and if my two stroke at home actually is a Johnson/Evinrude Sea Horse 5 Hp then it has virtually the same power to weight ratio as the lightest Chinese four stroke.
Interested to read that your friends have found the four strokes less reliable than the two strokes though, that's good information to have.

One question I forgot to ask earlier; what do you think of 360 degree steering with a forward/neutral gearbox as opposed to 180 degree with a forward/neutral/reverse box?

 

[Twister_Ken]

One question I forgot to ask earlier; what do you think of 360 degree steering with a forward/neutral gearbox as opposed to 180 degree with a forward/neutral/reverse box?

360 steering is pretty universal on the smallest o/bs. Maybe to do with weight saving?

 

[onesea]

Thanks again.
I doubt whether a 2 Hp would be powerful enough considering the weight of the boat and the tide and current in my local estuary.
I know that a two stroke theoretically gives more power per kg, but on the flip side modern four strokes are much more fuel efficient and nearly as powerful per kg, and if my two stroke at home actually is a Johnson/Evinrude Sea Horse 5 Hp then it has virtually the same power to weight ratio as the lightest Chinese four stroke.
Interested to read that your friends have found the four strokes less reliable than the two strokes though, that's good information to have.

One question I forgot to ask earlier; what do you think of 360 degree steering with a forward/neutral gearbox as opposed to 180 degree with a forward/neutral/reverse box?

My answer here would be 3.5hp 2 stroke would be ideal if you can get one. Unless you want to plane you really are not going to get THAT much more speed (unless battling very big head winds). As far as I can see its a hull size issue...

Mine pushes a 24' sailing boat at 4 knots in flat weather.

IMHO Most tenders are over powered, smaller lighter easier to carry ae good things. 25kg 4 stokes are not and not as reliable either...

 

[Quandary]

I have a Yamaha 2hp 2stroke petrol outboard. Very light at 25lbs. An older outboard but very reliable and easy to maintain. My Granda used to be a Yamaha dealer so I would be cuffed around the lugs if I used anything else

In Comber? I bought an 8hp. Yamaha from there in 1974 or thereabouts.

 

[JClarkes]

In Comber? I bought an 8hp. Yamaha from there in 1974 or thereabouts.

Yeah thats the place. Albert Clarke Marine. He's retired now.

 

[jwilson]

I've just bought a new 2.6m slatted bottom inflatable dinghy, I haven't actually seen it yet as I'm at work, but from the figures given I'm assuming it's got quite big tubes as its rated capacity is 450 kg.
Unfortunately, the website blurb doesn't give a maximum Hp/weight for the outboard, so what size engine do you think would be suitable for pottering around a fairly well sheltered estuary which has occasional currents of up to maybe 4 knots when they open the hydro power sluices one mile upstream.
Also any recommendations?

Thanks,

Paul

Secondhand 3.3/3.5 two-stroke. I use one on a 2.6 slatted-bottom anad a 2.7 inflatable floor dinghy: both plane nicely one-up at maybe 10 knots if you trim right. I'd use a 4 or 6 hp if I had one, but the extra weight would be a nuisance, and 6 is really too much power. As soon as you put two aboard forget planing, though you will get 5-6 knots or so and wet at full throttle.

If buying an engine I would not go past a 3.5 hp, and definitely go for a good used two-stroke.

 

[PaulJS]

Thanks to everyone for the advice. A 3.5 Hp 4 stroke is looking favourite despite the recommendations for 2 stroke, simply because I don't want the hassle associated with mixing 2 stroke oil/fuel in such small quantities, and I'd like to get something with a meaningful warranty... ie not a brand new updated 2 stroke from eBay!

 

[CAPTAIN FANTASTIC]

I bought a new Mercury (Tohatsu) 3.5 hp 4 stroke last year, very reliable engines but not the lightest. The problem is the flat bottom inflatable; although they only need very little power to move them along, they can not go fast because when you open the throttle the bow digs in and you can get very wet; hence a 3.5 hp will be wasted on this type of inflatable. The V inflatable bottom is by far superior and similar price.