Outboards - Dinghy and Back up for small Yacht

[steveej]

Hypothetical question.

Boat has a longshaft outboard that sits in a well.

Would like to buy a dinghy and outboard. Dinghys are obviously better with a short shaft outboard to reduce the chance of grounding the prop, but would it be possible to use a longshaft? That way I would have a backup if the main outboard failed.

The dinghy outboard is 3.5HP. The minimum recommended outboard for boat is 4HP so I am a little way off but it is better than nothing.

Any opinions?

 

[Tranona]

Don't use the long shaft on a short shaft boat. Not only will you suffer grounding problems, but on some you will get difficult starting and the dinghy will probably be unstable as the thrust of the propeller is too low. Think you will find 4 hp is maximum, not minimum on a dinghy unless it is a big heavy hard one. Stick to rowing.

 

[CAPTAIN FANTASTIC]

I have a 6hp four stroke Tohatsu long shaft which I use on an inflatable dinghy and as a back up for the yacht. The dinghy goes very well with the outboard, it doesnt cavitate at all.

 

[steveej]

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

 

[fredrussell]

Funnily enough I had the same idea. Boat (23ft) runs on 8hp outboard. I've been given a 3.5hp Tohatsu long shaft which I intend to use as tender motor and as emergency backup for boat. My plan was to make a outboard bracket that sits a bit higher on tender to offset the longer shaft.

 

[doug748]

I would not get a long shaft steve. Heavy, a pain to transport dodgy on a beach

The short shaft Tohatsu will push your boat along fine in light conditions if you attach it to the dinghy and lash the dinghy alongside.

 

[dylanwinter]

I would buy the longshaft

D

 

[Tranona]

I would buy the longshaft

D

Why buy the incorrect motor when the primary use is for a dinghy which requires a short shaft? Still perfectly possible to use it as a back up (who needs a second back up anyway?) by mounting it on a board at the correct height on the yacht. The compromise should be on the secondary use not the primary.

 

[steveej]

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.

 

[steveej]

weight is not an issue as it is the same size and weight as the 2.5HP

 

[seaangler23]

For me I'd go for a long shaft as even if it's a secondary use I'd rather have a back up engine that won't lift out the water in a swell as much when you really need it to get you out a fix, been there and done it with a short shaft and now I have a 5hp honda 4 stroke long shaft as an aux on my 23ft inboard motor boat and it's really good, I can use it on the dingy but I tend not to as its a compromise and you can feel it levering one transom more than a short shaft, but it does cope

 

[Arcady]

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.

 

[HenryEDM]

I would agree that the priority should be for the primary use so a short shaft would be my suggestion. If you want to use it as a back up then a transom mounted bracket would be a possibility rather than relying on lashing the tender alongside. I have tried towing my 26ft yacht with my 2hp honda and got it to move forward against a 3 knot tide (whilst still attached to my mooring) so I reckon your 3.5 will be fine as a backup. What I'd think about are the likely scenarios when you'd need it: little or no wind and main engine fails is only one i can think of. In this situation dropping anchor and lashing dinghy alongside would be straightforward.

 

[steveej]

Yeah I like this in terms of pragmatism over theory.

scenario 1; heavy weather, engine goes down, you have wind so sail home or to a port of refuge
scenario 2: good weather, engine goes down, lash the dinghy. It might be a bit uncomfortable but were early 30's and used to physical hardship.

Am I missing something?

 

[Tranona]

Yeah I like this in terms of pragmatism over theory.

scenario 1; heavy weather, engine goes down, you have wind so sail home or to a port of refuge
scenario 2: good weather, engine goes down, lash the dinghy. It might be a bit uncomfortable but were early 30's and used to physical hardship.

Am I missing something?

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.

 

[jac]

Yeah I like this in terms of pragmatism over theory.

scenario 1; heavy weather, engine goes down, you have wind so sail home or to a port of refuge
scenario 2: good weather, engine goes down, lash the dinghy. It might be a bit uncomfortable but were early 30's and used to physical hardship.

Am I missing something?

Just the issue with waves. You may have a situation where the wind dies but it takes several hours for the swell to die down and in that time the boat may be pitching so much that the prop comes out of the water.

You also need to consider range under power with a jury engine. Do you carry enough fuel for say 6 hours of motoring. Best to view it as a way of getting from the point where you lower sails to a mooring rather than a way to motor the entire leg of a trip.

 

[steveej]

Just the issue with waves. You may have a situation where the wind dies but it takes several hours for the swell to die down and in that time the boat may be pitching so much that the prop comes out of the water.

You also need to consider range under power with a jury engine. Do you carry enough fuel for say 6 hours of motoring. Best to view it as a way of getting from the point where you lower sails to a mooring rather than a way to motor the entire leg of a trip.

There is an external fuel tank on board so this shouldn't be a problem for either short or long shaft. Provided we fill it up of course. They are both petrol so I don't believe this is an issue.

 

[Tranona]

There is an external fuel tank on board so this shouldn't be a problem for either short or long shaft. Provided we fill it up of course. They are both petrol so I don't believe this is an issue.

The biggest issue with using a standard shaft engine on a small yacht is that it ends up low down on the transom - exactly the reason why they usually have long shafts. This makes it difficult to reach the start and controls, but once you get it going it works OK. In the past when outboards were more common, the type of bracket that had adjustable height, usually by sliding on a track was useful as it allowed bothe size shafts to be used. Some of the cantilever brackets also have this facility. I had this on my Seawych which had a Seagull longshaft 110 as its normal engine, but I could lower it to use the short shaft 40+

 

[William_H]

With your main engine in a well it is unlikely that a short shaft engine will work in the well. So first off find if this is the case or not. It should be reasonably easy to raise the motor board on the dink to suit a LS motor. Even if you compromise and raise the motor about 50mm ie half the difference.
If you are prepared to fit a transom bracket for the o/b on the ship then get an adjustable height type so that you can raise it for starting and fitting the SS motor but can lower it enough for coping with pitching in waves or with someone on the foredeck (picking up a mooring).
Re using the dinghy and motor to tow the ship lashed to the side. Fine if you always tow the dinghy but not if you leave the dinghy attached to the mooring as I always do. So much depends on your situation. good luck olewill

 

[VicS]

There is an external fuel tank on board so this shouldn't be a problem for either short or long shaft. Provided we fill it up of course. They are both petrol so I don't believe this is an issue.

both 2 strokes or both 4 strokes presumably. Otherwise you will have to use 2 stroke mix for both

I may have missed what make the main engine is but if the two are different make s the fuel line connectors will probably be different.

It would have been a good idea if in your opening post you'd told us what boat you have. People might then have some idea as to whether a short shaft engine would work in its well.