Outboards - Dinghy and Back up for small Yacht

[GrahamM376]

The yacht minimum outboard is 4HP.

The outboard I'm buying is a 3.5HP tohatsu where the main use is for the dinghy.

My thinking is that if I get a long shaft I can use it as a back up to the main yacht engine.

Provided it works in the dinghy of course

We shifted a 34 ft boat quite a few miles in calm conditions with short shaft 2hp on dinghy tied alongside.

 

[seaangler23]

No. Most boats have no problem with two sources of power - sails and an engine. A second engine is really a redundancy. The only time in nearly 40 years I have needed a third source I did exactly what you propose. An Avon Redcrest alongside powered by a short shaft Seagull 40 plus (standard yotty fare all those years ago!) to move 3 1/2 tons of boat into shallow ater so that i could clear the bit of net of the prop.

I must admit to having a chuckle every time this subject comes up. The makers of boats and outboard motors go to great lengths to ensure that they are made with the correct shaft length - but all to no avail when there are wags on here that tell you the exact opposite of what is recommended is OK - or even preferred. Good thing they are not in positions of responsibility or accountability.

The great thing about forums is that people can share their experiences, no one needs to be insulted because you have a different opinion.
When I do anything to my boat i try to build it for the worst case scenario and in my experience for an outboard to be considered a back up regardless of how many fail safes and assuming its on a transom bracket on a small boat then it should be a long shaft, and in my experience a long shaft can be used albeit not ideally on a dingy with a few considerations, these are small engines and small speeds.
Also in my opinion people who think outside the box and adapt should be charge, not those who can quote a manual.
On a lighter note I still own a seagull and had it on my dingy for a run recently, it's a long shaft and I lived to tell the tale,

 

[doug748]

so we have a 50/50 split opinion so it seems.

lets assume my cruising area is the Bristol channel, half way out in the Bristol channel my engine goes kaput. Is it really feasible to lash the dinghy to the yacht?

Genuine question.

As the others have said, yes, it works well.

The dinghy tends to articulate with the waves and keeps the prop in it's proper place. I have brought a 4ton boat home with 2hp setting the outboard running and steering with the boat's tiller.

 

[Tranona]

The great thing about forums is that people can share their experiences, no one needs to be insulted because you have a different opinion.
When I do anything to my boat i try to build it for the worst case scenario and in my experience for an outboard to be considered a back up regardless of how many fail safes and assuming its on a transom bracket on a small boat then it should be a long shaft, and in my experience a long shaft can be used albeit not ideally on a dingy with a few considerations, these are small engines and small speeds.
Also in my opinion people who think outside the box and adapt should be charge, not those who can quote a manual.
On a lighter note I still own a seagull and had it on my dingy for a run recently, it's a long shaft and I lived to tell the tale,

You are missing the point. There are very sound reasons why outboards and boats are made to match each other - if it were not the case, why bother if the user can do what he wants?

The OP wants a motor for his dinghy, which he MIGHT use as a back up for his yacht. Why buy the wrong motor for a secondary that may never happen, and can be accommodate by small change to the boat.

There is a world of difference between "thinking out of the box" and ignoring the sound advice of experts (not me - although was responsible for such things at an outboard manufacturer many years ago) in the field.

 

[lw395]

I've seen people using longshaft motors on inflatables, if you open the throttle, it tries to fold the boat in half.
It's the leverage of the prop being lower in the water.
I would get the smallest, lightest o/b I could find for the tender, unless I knew I would frequently go a longish way in the tender.

Anything that makes the tender less hassle to use is good, particularly where SWMBO is involved.
You don't want to be breaking shear pins at midnight getting back to the boat because your motor needs too much water.

 

[steveej]

Thanks for everyones input on this.

I have decided to go with the short shaft and experiment with lashing the dinghy. If that doesn't work to well I can stick a sliding bracket on the Yacht transom.

 

[VicS]

Thanks for everyones input on this.

I have decided to go with the short shaft and experiment with lashing the dinghy. If that doesn't work to well I can stick a sliding bracket on the Yacht transom.

You might have difficulty finding a bracket that will lower a short shaft engine far enough on your transom. Also being dangled a foot or so aft of the transom means that in a bit of chop the tendency for the prop to be lifted out of the water and lose all drive is increased.
I had a short shaft engine on my Seawych at first. I soon realised that a long shaft was a much better idea. OK in flat water hopeless other wise.
The dinghy alongside is also only practical in calm conditions.

is there any possibility that you can use the short shaft engine in the well. It will be better than dangling off the transom if you can!

 

[GrahamM376]

Thanks for everyones input on this.

I have decided to go with the short shaft and experiment with lashing the dinghy. If that doesn't work to well I can stick a sliding bracket on the Yacht transom.

Good decision I think, I tried a long shaft 9.8 on our 2.9m inflatable, it was a pain coming onto beaches and a bit unstable under power so converted it to short leg. One point about towing alongside, you will need to be in the dinghy (or have heavy weight in its bow) to stop the bow rising under power.

 

[steveej]

is there any possibility that you can use the short shaft engine in the well. It will be better than dangling off the transom if you can![/QUOTE]

It may well be an option which I can try

 

[graham]

We have a 3.5 long shaft tohatsu that goes on the dinghy or pushes the boat on a transom bracket.
Sure you have to be carefull you don't ground the outboard when used on the dinghy but you have to be carefull you don't ground the outboard whatever length the shaft. In practice it works fine.Our kids used to spend hours motoring about in the tender without wrecking the prop.

On the yacht it pushes our heavyish 25 footer fine in quiet weather , more powerfull than you would expect.


Personally based on our own experience I would go for the long shaft.

 

[ayzek]

According to what the others says from they experience , your boat will sail good enough with this outboard. But I recommend for you to add a shim or something else to your transom in order to raise your outboard to the right level.
You may see that your dinghy sail good enough without this shim, but with this raising your boat go better. You may see the difference in heavy weather...

 

[jwilson]

It depends on the dink. Can you increase the transom height? A few small dinks are designed for longshaft outboards (http://www.portlandpudgy.com/yacht-tender/inflatable-boats_dinghies-faqs/). Personally I'm with Dylan - buy an engine to suit the boat and modify the dinghy if you can. I have previously used a longshaft outboard on a softail Avon Redcrest - not ideal, but neither was it impossible, just occasionally a bit more limiting.

Me too - longshaft 4hp on an Avon Redstart: a bit difficult to start due to back pressure on exhaust, worked OK at low revs, but almost folded up the dinghy at full throttle - too much leverage on dinghy transom mount. Only tried that once. On my other dinghy, a 7 ft hard-chine pram, it worked better except that if you gave it full throttle it could actually submerge the transom. Only did that once too. On a calm river Axe at W-s-M you could steadily open the throttle till at about 3/4 the transom was an inch above water and go up or down-river with a substantial wake.