What engine power do I need for my boat?

[Tiger Moth]

I have acquired a Caravela 22, it displaces about 1,200kg. There is a nice 4hp Tohatsu 4-stroke for sale near me, do folks think it will push the yacht along at hull speed? I'm not after vivid acceleration, just the smallest outboard that will do the job so I can lift it out of the well and stash it inside the cabin when moored.

 

[Snowgoose-1]

I have acquired a Caravela 22, it displaces about 1,200kg. There is a nice 4hp Tohatsu 4-stroke for sale near me, do folks think it will push the yacht along at hull speed? I'm not after vivid acceleration, just the smallest outboard that will do the job so I can lift it out of the well and stash it inside the cabin when moored.

4hp should be ok but unlikely to push you to hull speed.

The same Tohatsu 6hp would weigh the same as the 4hp so 6hp would be ideal.

Your might be able to but a saildrive prop that would be even better.

Hull speed is nice but you will be burning lots of fuel. Reducing by about 1 knot would be more fuel efficient and less smoke and noise in the cockpit because of the well.

 

[Pye_End]

Huge difference between flat water/no wind and trying to pound into a sea.

 

[Mark-1]

I've got a bilge keel Corribee which is similar size.

I use a 5hp 2T engine with a high thrust prop (ie a lower gear prop for no planing boats). I never have it flat out.

I also have a Tohatsu 3.5 2T with standard prop. It works fine but feels less powerful, I'm sure due to the prop. It's still pushes me along fine.

Both engines work fine for me and in a chop an outboard without a well is pretty crap, anyway. So the 4hp will ok, I'm sure.

My thoughts: If you're buying used, a 2T will be lighter and as as others say, if the 6 is the same weight as the 4 you might as well hold on for a six. Finally outboards are like currency, you'll sell if for what you paid. So buying this one and swapping it for something better later is a viable strategy.

Good luck, and great username!

 

[Stemar]

On my Snapdragon 24, the 3.5 2T from the dinghy pushed it along nicely when the big engine was sulking as long as the water was reasonably calm, but a long shaft would have been better when things got bumpy, as it would have kept the prop in the water better.

I think Snowgoose's suggestion of a 6hp, with more power for the same weight would be the ideal choice, but most of us are constrained by our budgets and, if the 4 is what I could find, I expect I'd go with it.

 

[doug748]

I have acquired a Caravela 22, it displaces about 1,200kg. There is a nice 4hp Tohatsu 4-stroke for sale near me, do folks think it will push the yacht along at hull speed? I'm not after vivid acceleration, just the smallest outboard that will do the job so I can lift it out of the well and stash it inside the cabin when moored.

I would go for it if the price is ok. I agree with you, on this type of boat ( unless you are thinking of big trips ) go smaller rather than bigger.

Wells can be tricky so check that it is immersed ok on both tacks. You can get a build up of gases, so a four stroke is preferable; in a following breeze a two stroke can be trouble.

.

 

[MisterBaxter]

Smaller is definitely better for outboards on small yachts, you lose most of the advantages of an outboard if you can't pick the thing up easily. And a heavy outboard on a wobbly bracket can quickly become a liability, although you've got a well so spared that problem...
But as mentioned, there's not much to dislike about a more powerful outboard that weighs the same.

 

[Geoff Wode]

The 4-6hp Tohatsu/Mariner/Mercury 4 stroke weigh around 23kg. Any more weight makes things unmanageable.

High thrust prop is an essential imho.

The carb on your potential buy might be on its way out. You could upgrade it to the 6hp carb.

 

[B27]

If the OP has spotted a tidy engine at a fair price from a local seller he tends to trust, then that's a reasonable proposition IMHO.
You may wait a long time to find a slightly more optimum model in good nick.

I'd rather have a 4HP which I trust than a 6HP which has been abused.
For a boat like that, I'd guess the advantage of a 6 over a 4 is unlikely to be so great I'd want to pay hundreds more.

I would check out the availability of props with less pitch.

 

[Tiger Moth]

Thank you all, your views are much appreciated.

 

[William_H]

Yes as said low power o/b is fine. I have just moved to a Honda 2.3 for my 21 fter. it is very adequate in calm conditions. Which is what I want it for. Boat sails nicely in any wind. Previously I had a Johnson 6 HP which one night towed my boat plus 2 x 24 fters home when becalmed. Not hull speed but quite fast enough.
NB " Hull speed " is a bit of a variable quantity being a range of speeds where an increase in speed becomes disproportionately harder to achieve. It is roughly described as square root of water line length in feet with a margin of about 20% on top of that which is reasonably achievable. 10% on top easy 30% on top almost impossible. So for OP 4 knots easy 5 knots possible 6 knots very hard 7 knots impossible. ol'will

 

[Stemar]

Absolutely. My 3.5 OB would push the Snappy along at a 4-5 knots, the 28hp (yes, I know, but it was free when I needed a new engine) could get up to 7 with a clean bum, but I left the same kind of wake that that stinkpotter leaves because the speed limit is 10 knots, so he's just off the plane

 

[38mess]

I had a 3.5 ob as back up on my 24ft fishing boat. It was on a bracket, It seemed fine on the rare occasions I used it. But any chop and the prop comes out of the water and you go nowhere.

 

[Snowgoose-1]

I have taken a snap of the standard and Sailmate props. Click for larger scale.
AFAIK, the Sailmate is a direct fit for 4/5/6 hp 4T Mercury/ Tohatsu /Mariner and possibly Yamaha .
The Sailmate prop has slightly more diameter, and has the "Mickey Mouse" ears with more pitch.

I'm in a tight marina and the Sailmate is brilliant in reverse and propwash . The standard prop is obviously less drag under sail, but in flat water the standard prop can be slightly faster but not so good for low grunt situations.

 

[Tiger Moth]

I have taken a snap of the standard and Sailmate props. Click for larger scale.
AFAIK, the Sailmate is a direct fit for 4/5/6 hp 4T Mercury/ Tohatsu /Mariner and possibly Yamaha .
The Sailmate prop has slightly more diameter, and has the "Mickey Mouse" ears with more pitch.

I'm in a tight marina and the Sailmate is brilliant in reverse and propwash . The standard prop is obviously less drag under sail, but in flat water the standard prop can be slightly faster but not so good for low grunt situations.

That's really helpful, thank you. With the engine in a well I can't crank it up out of the water so I think I'll do with the standard prop, I can't be doing with too much drag. I wonder if you can get a folding prop for an outboard? I'll investigate.