Which outboard for this dinghy?

[pwillems]

Hi all. I'm just in the polishing phase of restoring my new to me dinghy and am shopping for a new outboard. The dinghy is an Aquapro Monaco 341 (11 ft), which weighs 155 kg (340 lbs) dry hull. The plate on the back says it can take an outboard up to 40 hp.

Now, while I am certain that 40 hp on this boat is going to give a thrilling ride, what I am not certain of, is if I go for a much lighter (and cheaper) 30 hp will it be good enough for my purpose which is to take the family (2 adults, 3 kids) exploring and at a pinch, tow the mother ship out of a sticky situation should the need ever arise. I have no need to get around at 35 kn, but I do want to be able to get on the plane easily with the entire family aboard.

What are your thoughts on engine size looking at the specs above?

[a64pilot]

Properly propped my belief is that 30 hp would work.
Back in the early 50’s my Parents used to ski behind I think 25 HP.

[Oceanride007]

Just giving your post a kick along but my initial thought is even 30Hp is still too much. I'm doing a similar calculation on a smaller size, have had good guidance from manufacturer and also engine supplier.

Mind you some of us would prefer to urr on the small size as engine weight on a Davit is a consideration. Somebody once told me 50HP per ton might get you to plane, 65HP will. But not sure if thats a us Ton or one of ours.

Have seen a small family 2 children two adults happy with a 15HP 2 stroke Yamaha. But it does make a difference between 2 stroke and 4, ie I think the 2 stroke has more torque down low, ie a 4 stroke of same HP may not get you over the Power/speed hump apparent on a appropriate power curve. So would think if you go 4 stroke you need a few more horses.

[accomplice]

Having been through 5 outboards in the last four years, my advice is to select EFI first, a brand whose parts are available where you cruise second, and HP (vs weight) third.

[davil]

dIn the past I have under powered every mobile object I owned,that includes cars,sailboats,dinghies.
After a life of constant regret and frustration at been "underpowered" I concluded my next project will consider,the biggest motor I can,
Afford
Carry
Lift
Is surprising how little difference is for instance in weight between a given HP and the next,or price to that effect.
The load you contemplate is considerable (although not sure how many pounds) and also do not know what where you plan to use your tender.
However,during my cruising I constantly cursed my under powered status.
Your plan to assist the "mother ship" is always a possibility,I used my inflatable with a 4HP outboard to move my Tartan 34 out of the Lee in Anacapa when my Yanmar died,it worked,on the other hand I envied every cruiser I met that could just zoom out and plane while I was "moving so slow""
Go for the biggest you can afford,carry and lift.
That is what I will do next
My two cents opinion and worth each one.

[DeepCut]

I think 40hp will be much harder to manage than a smaller HP outboard when removing it from dingy...
Also consider a 40hp will be much more attractive to those who want to "borrow" your outboard compared to all the smaller engines nearby.

[HankOnthewater]

Just going though the same exercise on a boat for a friend on his 54 ft boat: a 30 Hp Honda weighs ~75 Kg (with oil), without fuel, you might need 2x 20 lt of that.
A 15 Hp Yamaha (enduro or not) is what many believe the best general workhorse, but am not sure if that 15 HP will get you on the plane with 5 on board. Maybe you can borrow an outboard that you think fits the bill, to try it out.
If you want to try a Yamaha 15 Hp, you can borrow mine.

Are your davits stout enough to lift 155+75+40=270 Kg, or do you have to remove the fuel and take the engine off? Do you have block and tackle ie on small crane to lift that engine? Even a 15 Hp Yamaha that weighs 36 kg, is too heavy to lift without mechanical assistance.

Bigger outboards like the Honda, the 30 HP Yamaha (55 kg for 2 stroke) and Suzuki (?74 kg) come with an alternator, and you might want to fit a battery as well, hmmm another 15-25 kg, and some of these engines may NEED a battery.
Hand (pull) starting such engines maybe possible, but more difficult than a smaller engine.

[pwillems]

Originally Posted by davil

Go for the biggest you can afford,carry and lift.

Well the price difference between the 30 and 40 I am considering is actually very significant. Though similar in appearance, the 40 jumps to the big boys category with clever NMEA electronics etc and the price jumps up around 40%.

As for carrying/lifting, the mother vessel is a big girl with big solid davits. I don't know how much they can carry, but by looking at them, I'd say the 20 kg weight difference does not come into play in this case.

Originally Posted by DeepCut

I think 40hp will be much harder to manage than a smaller HP outboard when removing it from dingy...

At this size, outboards are permanently bolted through the dinghy transom, it will be on the dinghy while handing from davits.

[pwillems]

Originally Posted by HankOnthewater

Just going though the same exercise on a boat for a friend on his 54 ft boat: a 30 Hp Honda weighs ~75 Kg (with oil), without fuel, you might need 2x 20 lt of that.
A 15 Hp Yamaha (enduro or not) is what many believe the best general workhorse, but am not sure if that 15 HP will get you on the plane with 5 on board. Maybe you can borrow an outboard that you think fits the bill, to try it out.
If you want to try a Yamaha 15 Hp, you can borrow mine.

Are your davits stout enough to lift 155+75+40=270 Kg, or do you have to remove the fuel and take the engine off? Do you have block and tackle ie on small crane to lift that engine? Even a 15 Hp Yamaha that weighs 36 kg, is too heavy to lift without mechanical assistance.

Bigger outboards like the Honda, the 30 HP Yamaha (55 kg for 2 stroke) and Suzuki (?74 kg) come with an alternator, and you might want to fit a battery as well, hmmm another 15-25 kg, and some of these engines may NEED a battery.
Hand (pull) starting such engines maybe possible, but more difficult than a smaller engine.

Yes to all of that, the dinghy is a forward steering console type with built in fuel tank, nav lights, etc... Therefore engine will be remote steer with electric start etc... Weight is always a concern, but looking at the custom built davits (100 * 50 mm box section), I'm confident it will be fine.

[HankOnthewater]

Originally Posted by pwillems

Yes to all of that, the dinghy is a forward steering console type with built in fuel tank, nav lights, etc... Therefore engine will be remote steer with electric start etc... Weight is always a concern, but looking at the custom built davits (100 * 50 mm box section), I'm confident it will be fine.

That is good then. The reason for the steep weight/ price rise going from 30 to 40 HP could be that Honda and Suzuki both using larger engine blocks for the 40 HP, while Yamaha the displacement is the same for these two HP.
It is likely that you end up well over 300 kg for the total weight once you add fuel, anchor+some chain and line, oars, safety gear, ropes, battery and sundries.

Can I ask another question, and not intending to rain on your parade, can the dinghy be hoisted high enough not to be hit by waves? Have you sailed with that dinghy in the davits in adverse weather?

Even with a big boat like yours, 300 kg beyond the stern might influence your waterline, how your boat sits in the water. Hmmm, 300 kg may be only 1% of your displacement. Just some thoughts, you may have played with already.

[Oceanride007]

Any chance of you borrowing say a 20hp and see how it goes. ?

What is the maximum weight you are prepared to go.? Would you carry the Engine on the dinghy? I doubt too many experienced sailors would want to even carry the dinghy on its own.

Up at Airlie, lots of bareboats with Ribs over 3m (to get surveyed) thay all have 6HP motors, they will all plane, the RIBs will take up to 10 people with a inverse probability of planing. Funny thing is that 6HP may have trouble with 2.5m.

You won't get a definitive answer unless you can get the powercurve requirement of your particular hull.

But if you could be happy with planing with half your complement and be a displacement boat the rest, I believe that would be more sustainable.

[pwillems]

Originally Posted by HankOnthewater

Can I ask another question, and not intending to rain on your parade, can the dinghy be hoisted high enough not to be hit by waves? Have you sailed with that dinghy in the davits in adverse weather?

Yes, comfortably. I haven't sailed with this dinghy yet, but with another of similar size. Really not too concerned about carrying the dinghy around, more concerned with getting the right engine for the intended purpose which is to get the family around at reasonable speed and at a pinch act as a tug for the big boat.

[a64pilot]

Electric start, battery, center console etc., it’s going to take every bit of 30 hp.
My 3.10 RIB with a 20 HP Zuki when propped to go fast, (12” pitch) will barely crawl onto plane with two large adults, but it’s fast. Propped for power (10” prop) it leaps onto plane with four large adults and hits the rev limiter at about 25 kts or so.
11” is just right for us, prop pitch makes a huge difference, but our 10.5 RIB is not overpowered in my opinion with 20 HP.

[GordMay]

FWIW: The "Monaco" range is designed specifically for high horsepower outboards with long shaft, electric start, and power tilt/trim.

[messias]

20hp 2stroke will get you on the plane... 4stroke will be much heavier