what power outboard for rigid tender?

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Chae_73

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Today i had the inaugural launch of what hopefully will be our means of transport to our mooring. I had acquired a rather well used 3.5 hp Tohatsu 2 stroke for the occasion. This lasted about 3 mins before overheating and dying - fortunately it owes me nothing.

So looks like i will have to get a 4 stroke. The tender is GRP, 12' long, heavyish, can accommodate 4 reasonably safely. I see that Suzuki 4 strokes are all the same weight up to 6 hp. Is there any reason to get less than 6 hp than to save a small number of £?

many thanks.
 
Chae_73 said:
So looks like i will have to get a 4 stroke. The tender is GRP, 12' long, heavyish, can accommodate 4 reasonably safely. I see that Suzuki 4 strokes are all the same weight up to 6 hp. Is there any reason to get less than 6 hp than to save a small number of £?

many thanks.
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Fuel consumption may be higher, if the dinghy has a maker's plate which specifies less than 6 dobbins and you have a horrific Speed 2: Cruise Control style accident I suppose some ambulance chaser might sue you. Seems unlikely with a dinghy that big though.
 
Faced the same choice for our inflatable-went for Yamaha 6hp but Suzuki was second choice -just thought Yamaha felt more robust but personal choice . You will find they use more fuel than the unreliable 2 stroke but maybe a reserve tank from marine superstore is answer (much cheaper than branded ones) only other issue seems to risk of hitting prop on your shiny newOB of whatever make whereas split pins are cheap on 2 strokes I’ve had. You might get a tiller extension to sit further forward if you don’t have ballast to place in bow I suppose.
 
Chae_73 said:
Today i had the inaugural launch of what hopefully will be our means of transport to our mooring. I had acquired a rather well used 3.5 hp Tohatsu 2 stroke for the occasion. This lasted about 3 mins before overheating and dying - fortunately it owes me nothing.

So looks like i will have to get a 4 stroke. The tender is GRP, 12' long, heavyish, can accommodate 4 reasonably safely. I see that Suzuki 4 strokes are all the same weight up to 6 hp. Is there any reason to get less than 6 hp than to save a small number of £?

many thanks.
Click to expand...

You'll save a lot of £ and kg if you can keep below 4hp.
 
Thanks all. Fuel consumption is not a big issue for the amount of use it will be getting; reserve tank sounds like a sensible extra.

Kelpie, below 4 hp isn't out of the question but considering the tide rip between the slip and the mooring, I'm thinking that more power could be useful, especially when loaded, Today there was just my 15 year old son and me in the boat, and we made steady progress against the ebb with our 3.5 (until it expired), but it was nowhere near planing.

what is the weak link in a 4 stoke outboard prop if not a shear pin?

Edit - bought the dingy second hand and it has no plate on it so no idea what the design limit might be.
 
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ashtead said:
Faced the same choice for our inflatable-went for Yamaha 6hp but Suzuki was second choice -just thought Yamaha felt more robust but personal choice . You will find they use more fuel than the unreliable 2 stroke but maybe a reserve tank from marine superstore is answer (much cheaper than branded ones) only other issue seems to risk of hitting prop on your shiny newOB of whatever make whereas split pins are cheap on 2 strokes I’ve had. You might get a tiller extension to sit further forward if you don’t have ballast to place in bow I suppose.
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Do 4 stroke O/Bs not have shear pins?
 
Much depends if you want to plane or not. But if not then I’d just get an electric. They’re expensive but massively beneficial on some many counts. Since getting ours we rarely use the petrol anymore.
 
I think electric would be great for taking on the boat to use on the inflatable tender, to get to the pub and (hopefully) back again, avoid cans of petrol on board, quite light for lifting off the tender into the boat. Fine for weekend sailing; not sure how it would pan out for more extended cruises but I like the idea.

I don't like the idea so much of 2 hp electric on a fully laden 12" grp boat against a 5 knot ebb tide out of the Deben with a bit of a wind blowing. But then, I've not tried it so maybe it would be fine .
 
Chae_73 said:
I think electric would be great for taking on the boat to use on the inflatable tender, to get to the pub and (hopefully) back again, avoid cans of petrol on board, quite light for lifting off the tender into the boat. Fine for weekend sailing; not sure how it would pan out for more extended cruises but I like the idea.

I don't like the idea so much of 2 hp electric on a fully laden 12" grp boat against a 5 knot ebb tide out of the Deben with a bit of a wind blowing. But then, I've not tried it so maybe it would be fine .
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We live aboard and been to using electric in canaries and azores frequently. It has masses of torque and even hard to rescue some frenchies in a gale when they couldn’t get back to their board in their tender. The yahama we have is great for when we want long distance and fast at 13kts but still it’s the Torqeedo that is the work horse. Here’s my 2 pence:

Going Electric! | Chasing Contours
 
Chae_73 said:
a 5 knot ebb tide
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Surely a dingys max hull speed would not let you go fast enough to make decent headway without sinking yourself?
Can certainly get dingys to plane with enough power but it's not always the safest.
If your dingy won't plane then 6 hp must be wasted power as it will just dig the stern in more and create a larger wash?
I managed 12 knts in a tiny inflatible with an inflatable keel and floor and a tohatsu 3.5 2t pre pandemic. Now I've gained a least 10kg and have no hope of planing ?
 
Chae_73 said:
Today i had the inaugural launch of what hopefully will be our means of transport to our mooring. I had acquired a rather well used 3.5 hp Tohatsu 2 stroke for the occasion. This lasted about 3 mins before overheating and dying - fortunately it owes me nothing.

So looks like i will have to get a 4 stroke. The tender is GRP, 12' long, heavyish, can accommodate 4 reasonably safely. I see that Suzuki 4 strokes are all the same weight up to 6 hp. Is there any reason to get less than 6 hp than to save a small number of £?

many thanks.
Click to expand...
Is it a displacement dinghy? I had a 13ft Orkney type GRP dinghy. I had a 5hp Mariner 4 stroke which never needed more than half throttle. After that is was just noise and vibration but never more than 5.5 knots.
 
Caraway said:
Is it a displacement dinghy? I had a 13ft Orkney type GRP dinghy. I had a 5hp Mariner 4 stroke which never needed more than half throttle. After that is was just noise and vibration but never more than 5.5 knots.
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I must admit that I have assumed it will plane but I could be wrong. It's just a big grp rowing boat thing. What essential characteristics are required for it to plane?
 
You can get nearly anything to plane if you throw enough power at it ,excluding keeled boats.. but it may become very unstable and scary.. body weight positioning is very important in a small boat which often means you can't reach the outboard.
Your Orkney is certainly not designed to plane, but put a 30 on it and I would think 30 knts or death.?.. an oversized engine may be too heavy for the boat and the transom may struggle with being overpowered.
The hull is a v shape on planing hulls.
 
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Pretty unlikely it will plane. It has no chines to lift the hull over the bow wave and is round bilged. If the aft sections of the hull are flat (ish) it may manage to escape it's hull speed. But I doubt it.
 
Rappey said:
You can get nearly anything to plane if you throw enough power at it ,excluding keeled boats.. but it may become very unstable and scary.. body weight positioning is very important in a small boat which often means you can't reach the outboard.
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I do remember getting a Metzler inflatable to plane one very calm day off Cowes. You are right, I had to crouch down right in the v of the bow and couldn't reach the outboard. I was 17 at the time, and didn't think it particularly unsafe but would not attempt that now.
 
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