Outboard HP vs weight of boat

G

GreekYiannis

Well-Known Member
Joined
24 Sep 2012
Messages
82
Location
Saronic gulf
Visit site
I'm ready to fit an auxiliary outboard engine to my Colvic 20 [overall weight I think is 1.5 tonnes with full displacement hull] but can't find a formula of HP to weight / hull type etc. Does anyone know how to measure such things?
 
oops, didn't read properly.

For an auxiliary, I'd go for something like an 8hp.
Sorry, no formula or tables or science behind that suggestion.
 
Last edited:
It is more about the propeller than the hp of the engine. As suggested an 8hp would do the job particularly if you buy a "saildrive" version with a larger finer prop. You should be able to get displacement speed of around 5.5 knots in flat water.
 
Tranona said:
It is more about the propeller than the hp of the engine. As suggested an 8hp would do the job particularly if you buy a "saildrive" version with a larger finer prop. You should be able to get displacement speed of around 5.5 knots in flat water.
Click to expand...

I have a Tohatsu 6hp saildrive extra-longshaft, it's fantastic, they also make 10hp version. Make sure you get the ultra longshaft so that the prop stays submerged in choppy conditions; because the OB is hung on the back of the transom any pitching is exaggerated at the transom, which will kick the prop up out of the water.

I think Yamaha make a high trust 10hp, it's got a good reputation as well.
 
GreekYiannis said:
That's great advice - Thanks. Is your Tohatsu a 2-stroke or 4-stroke?
Click to expand...

It's a 4 str, and I chose it because at 25 kg weight it's about the heaviest you can man handle onto the transom without crippling yourself.

We do about 6kts a 3/4 throttle , but it is on a 1.5 ton cat.

as you can see from the photo, the long shaft is 'really ' an ultra longshaft!

View attachment 42844
 
You must log in or register to reply here.

Share this page

Top