What size auxcillary do I need to move my boat

[barryassheton]

Hi, I am new here and I need to move my uncles boat from langstone harbour to portsmouth harbour but the inboard engine has been removed. What size (hp) auxcillary outboard will move it. I have attached a picture of the boat, its 20' .

Thanks Baz

 

[MapisM]

What size (hp) auxcillary outboard will move it.

5hp will do.
I've seen boats similar to yours with a 15hp o/b as a MAIN (and often unique) engine.

 

[PaulGooch]

Just make sure the tides are working in your favour, not against you.

 

[landlockedpirate]

5hp would work if you are going with the tide and wave height is small, but I think I would want a little more to give a safety margin. I think 8-10hp would make sure you could reach hull speed if needed.

 

[CaptainMike1970]

I wasonce given a rule of thumb of "about 10% of the main engine hp", it should get you home if you use the tide to assist you.

 

[JKay]

5hp would work if you are going with the tide and wave height is small, but I think I would want a little more to give a safety margin. I think 8-10hp would make sure you could reach hull speed if needed.

I agree 10 minimum

 

[AndieMac]

In case the boat is a little basic as far as gear is concerned, eg radio, take a handheld VHF and spare batteries.

Make sure the prop shaft is secure (nip up the stuffing box bolts at least), with engine and gearbox out there might not be a lot holding it in place once underway, or charged batteries to run the bilge pump.

 

[MVP]

Blimey, the guy's only going from Langstone to Portsmouth, not round the world

 

[AndieMac]

Blimey, the guy's only going from Langstone to Portsmouth, not round the world

Unfortunately have heard of local boats being towed in similar circumstances, and losing the unattached shaft and smallish prop out past the off-set rudder once the prop spins and pulls backwards.
Besides the replacement cost of the hardware, you would have pressured water ingress through an inch and a half hole.

That could ruin your whole day....

 

[ontheplane]

I agree that 10-15hp would be ok - but try and make sure the prop is the right type.

Most 15hp motors have props designed for light inflatables and planning speeds, which clearly you are not going to achieve. See if you can get a finer pitch prop in order to maximise the thrust - better yet would be a "bigfoot" or "saildrive" engine which has a prop maximised to thrust rather than top end speed.