How Big?

Tony · 15 January 2007, 07:01

After spending the last 8 weeks mucking about around the islands in less than desirable conditions, i have decided that maybe an aux engine would be a good idea.The question is how big and what sort is powerful enough to push the boat home safely.
I have an 8m Scorpion with a 250DI
Thanks

Pete7 · 15 January 2007, 08:16

Tony, your Scorp will only travel at 6-7 knots at displacement speed (1.3 x the square root of the water line etc) so 10 - 15 hp will be fine unless you want to charge though the Alderney Race against the tide. A 4 stroke will enable you to connect the main take to the aux engine, a two stroke will need careful thinking about because of its 2 stroke oil supply, but will be lighter. Supply of new 2 strokes is now somewhat limited.

If your going second hand route ask to borrow it first, this would also confirm if you need short or long shaft.

Pete

BogMonster · 15 January 2007, 08:28

The rule of thumb is apparently 1hp per metre of boat so I guess 8hp minimum. Maybe a 9.9?

I needed a long shaft on my Humbug so I would think you'd need a long on a much bigger Scorpion.

Nick Hearne · 15 January 2007, 08:37

Tohatsu 9.8 two stroke, only 26Kg if weight is a issue?

Nick

Nos4r2 · 15 January 2007, 09:08

Personally I'd go for a 15hp and prop it right. At least that way waves hitting the bow won't stop you dead in your tracks. I prefer 1hp per metre up to 4m then 2hp/m and round up to next available size after that as a rule of thumb.

I'd have a bigger one for mine if I could fit it on the transom.

Tony · 15 January 2007, 09:15

Thanks
i think the Johnson 15hp looks ok?
http://www.brp.com/en/Products/Johns...?productID=J15

Ezgoing · 15 January 2007, 14:02

Tony

One of the problems I find wiht auxs is their ability to grip the water. For this reason I prefer the high thrust with the bigger prop and reduction gearbox.

Personally I took the aux off the boat on grounds
1 If weather really too bad I should not be out on my own.
2 If weather ok I should be able to anchor until help arrives

Above assumes i is keeping an eye on forecast and radio is working.

Rgds

Nos4r2 · 15 January 2007, 23:18

Quote:

Originally Posted by Ezgoing

Tony

One of the problems I find wiht auxs is their ability to grip the water. For this reason I prefer the high thrust with the bigger prop and reduction gearbox.

Personally I took the aux off the boat on grounds
1 If weather really too bad I should not be out on my own.
2 If weather ok I should be able to anchor until help arrives

Above assumes i is keeping an eye on forecast and radio is working.

Rgds

Calling the lifeboat out to tow you in is a bad thing to do if there's a safe way round it.

Do you guys have an equivalent of the RNLI in Eire?

Poly · 15 January 2007, 23:45

Quote:

Originally Posted by Nos4r2

Do you guys have an equivalent of the RNLI in Eire?

RNLI covers S. Ireland too.

BogMonster · 16 January 2007, 08:25

Quote:

Originally Posted by Nos4r2

Calling the lifeboat out to tow you in is a bad thing to do if there's a safe way round it.

Do you guys have an equivalent of the RNLI in Eire?

And if there isn't a lifeboat you are really in deep s***!

The only time I have needed my aux in anger was a few weeks ago and I was bloody glad I had it there and ready to go.