Quick outboard question

I think one of the crucial factors will be the weight of the engine if you intend to keep it inside the boat and only fit it for emergency use. So something in 3 or 4 HP might just be light enough. If you will keep it on the baracket then 6 or 8 hp in a long shaft might be better. This should give you 5 knots in still water. Note that any engine will give max water speed in still water. Any adverse tidal flow will simply move you and the water backwards relative to your water speed. So in practice a 4knot adverse current when you have 5knot water speed will result in 1 knot speed over the ground. The only way to improve that siuation is more engine power but then your hull speed will start to limit any increase in water speed. So trying to buck an adverse tide is not different from trying to go faster.
What does matter with engine power is the ability to make near hull speed in a strong head wind with or without waves. A tiny engine will really fall down under those conditions.
I have to say that if you have sails and a decent inboard engine that is well maintained you should not need an auxilliary auxilliary. I can go for a season without using engine at all. Infact I like to leave it home. good luck olewill

PS Hull speed is given as something like or a bit over the square root of the water line length in feet. So 22ft water line will have a hull speed around 4.5 knots. This is a speed which is easily acheived but where any further increase in engine power will give progressively less increase in speed. So you might easily get 5knots but hard to get 6knots and takes a lot of power to get 7knots much more for 8knots and probably never get any more.
 
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I have a Tohatsu 3.5 HP short shaft on my Macwester Rowan, 22 footer. Beam of 8 feet and weighs about 2 tons! The OB was the last thing I fitted before attempting first Channel crossing in the boat. Off Guernsey the inboard (old Petter Mini6) failed due to broken fuel pipe and we used the outboard for 8 hours to push us to St Peter Port. I think we had 2 knots of current against us, and made about 1.5 knots over the hour! I'd not want to go anywhere without a backup now, even with the Yanmar 1 gm 10 I have. The OB can get you out of all sorts of trouble.
 
William_H said:
PS Hull speed is given as something like or a bit over the square root of the water line length in feet. So 22ft water line will have a hull speed around 4.5 knots.
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That's rather low. It's usually quoted as 1.3 or 1.4 x the square root of the waterline length; I prefer to simplify to "the square root of twice the waterline length", so a 22 footer will have a hull speed of about 6.5 kt. However, the W22 has a waterline length of just over 18', giving a hull speed of about 6 kt.
 
JumbleDuck said:
That's rather low. It's usually quoted as 1.3 or 1.4 x the square root of the waterline length; I prefer to simplify to "the square root of twice the waterline length", so a 22 footer will have a hull speed of about 6.5 kt. However, the W22 has a waterline length of just over 18', giving a hull speed of about 6 kt.
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Yes, my 22 footer will reach 6.5 knots, and even 7+ at one time!

And that's the length OA, waterline will be less.
 
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I really wouldn't go down the long shaft route unless your tender will take it. You need your main engine to be reliable and from what you've said it is so buying a dedicated spare seems pointless.

My suggestion would be to get a larger ob for your tender, 4-5hp and then work out a way of mounting the ob on the yacht when all else fails. Did you see the YM article a couple of months back when TC moved a warrior using a 2hp o/b.

Don't worry about using the engine to fight the tide. That is what the main engine is for. Your contingency for engine failure should be sail/ anchor/ moor then wait for slack tide to manoeuvre the boat somewhere where the main engine can then be fixed.
 
jac said:
My suggestion would be to get a larger ob for your tender, 4-5hp and then work out a way of mounting the ob on the yacht when all else fails.
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The problem with that is a 4-5hp of the new type is very heavy and not a good engine for a tender to a 22' boat. On the other hand, if you look at the height of the transom of the boat, a standard shaft powerhead would be so far below the top that you would have to hang over the back upside down to reach the controls. Lousy compromise all round.

The outboard version of this design had a big cutout in the middle of the transom and a false transom separating it from the cockpit so it was feasible to use an outboard.
 
A small outboard for use on the tender and ' impulse power ' a la Starship Enterprise seems a good idea; BUT when I've tried my tenders' Mariner 2hp on my Anderson 22 it hardly moved her, despite the A22 being moderate displacement with a slippery hull shape.

A decent outboard to move the mother ship would be 4-5 hp just like the existing main engine, there's a limit to how many spares one can lug around and weight is the enemy of all boats !

I'd concentrate on the inboard being reliable, then if it should conk out one always has the sails and anchor; a small engine suitable for the tender might be useful for close quarters berthing.
 
Fair point re weight of a 4 stroke. Will def make sure I keep my old Tohatsu 2hp going well!!

I disagree re the long shaft though. This is an emergency engine, not the yachts auxiliary. If it was the proper auxiliary then long shaft is correct and probably more than 5hp to be fair.

OP has to have his main engine working reliably as others have stated. If that is so, how often will the Ob be needed. Modern Diesel engines treated ok last for ever. If he gets an ob that only works on the yacht then he is carting around hundreds of pounds worth of engine that may never be used and may be only intermittently tested. Whereas the OB for the tender will be useful, and tested every time he uses it for real so has greater chance of being working when needed.
 
An outboard on the transom has other disavantges; not only does it look awful, spoiling the lines of a boat, it is weight in exactly the wrong place.

Unless there are remote controls fitted it means facing aft to the controls, which almost guarantees one an entry on Youtube.

A transom mount also means of course that the prop is relatively easily & often pitched out of the water.

Another factor not often considered, but I have found on other peoples' boats and very relevant, is that when alongside a wall other peoples' shorelines may well get wrapped around the engine and rip off one's engine controls, which is a bit of a negative thing.
 
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Seajet said:
An outboard on the transom has other disavantges; not only does it look awful, spoiling the lines of a boat, it is weight in exactly the wrong place.

Unless there are remote controls fitted it means facing aft to the controls, which almost guarantees one an entry on Youtube.

A transom mount also means of course that the prop is relatively easily & often pitched out of the water.

Another factor not often considered, but I have found on other peoples' boats and very relevant, is that when alongside a wall other peoples' shorelines may well get wrapped around the engine and rip off one's engine controls, which is a bit of a negative thing.
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All very good points (and true ones) BUT

OP is asking about how to mount an OB IF his IB fails so looks, convenience etc go out the window. It should be about what are the simple changes/ tweaks are that OP can make to use an OB.

So having seen the last couple of YMs when TC moved a very large boat with a 2hp I'm also trying to work out how to do it with mine. I have no intention of re-engining a 36footer with a 2hp outboard but would be good to know I can do it to get her onto a pontoon at slackish if the engine fails.
 
jac said:
I disagree re the long shaft though. This is an emergency engine, not the yachts auxiliary.
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Have a look at the transom of that boat. Would you fancy hanging upside down to try and reach the controls when the bracket is down? The OP wants a get you home solution when things have gone wrong and a short shaft is just not convenient. If going to use a dinghy engine, then use it in the way described in the oft quoted article from YM. Lash the dinghy and motor alongside and you stand a reasonable chance of moving and controlling the boat.
 
Seajet said:
An outboard on the transom has other disavantges; not only does it look awful, spoiling the lines of a boat, it is weight in exactly the wrong place.

Unless there are remote controls fitted it means facing aft to the controls, which almost guarantees one an entry on Youtube.

A transom mount also means of course that the prop is relatively easily & often pitched out of the water.

Another factor not often considered, but I have found on other peoples' boats and very relevant, is that when alongside a wall other peoples' shorelines may well get wrapped around the engine and rip off one's engine controls, which is a bit of a negative thing.
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On the plus side. If you get a fishing line, rope or weed around your prop it is only a few moment's work to clear it.
 
Tranona said:
Have a look at the transom of that boat. Would you fancy hanging upside down to try and reach the controls when the bracket is down? The OP wants a get you home solution when things have gone wrong and a short shaft is just not convenient. If going to use a dinghy engine, then use it in the way described in the oft quoted article from YM. Lash the dinghy and motor alongside and you stand a reasonable chance of moving and controlling the boat.
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For a one off maybe. I agree that the dinghy alongside may be better but are you really suggesting that the OP buy an outboard that may never be used on the yacht as the IB never dies and can never be used on the tender as it's too big.
 
JumbleDuck said:
That's rather low. It's usually quoted as 1.3 or 1.4 x the square root of the waterline length; I prefer to simplify to "the square root of twice the waterline length", so a 22 footer will have a hull speed of about 6.5 kt. However, the W22 has a waterline length of just over 18', giving a hull speed of about 6 kt.
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You are quite right it is just that hull speed is not a clearly defined number. It is a point or perhaps an area on a graph of speed versus horsepower where the graph starts to get steeper exponentially from around this area known as hull speed. So at speed = square root of wl lenght it is very easy to drive the hull. at 1.3 times square root of wl lenght in feet it takes a bit more power but go to twice and you need real power. Now my little 21fter runs under engine at 5 knots quite happily with 6HP at fairly moderate power. It will do 9 knots under sail but who knows what the equivalent horsepower of sails and wind is. Quite a lot I would say. I expect disaster at any moment at that speed. olewill
 
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