Which engine for my dinghy?

[a64pilot]

Difference in engines between the 9.9 to 20 HP Suzuki is the computer, there are no mechanical differences. This has gotten real common. In fact Mercury’s large Verado outboards from 150 HP to over 300 HP are just two engines, with different computers.

In the US long ago the 9.9 was born when laws were passed banning engines of 10 HP and above from many lakes etc., so the manufacturers replaced the 10 HP stickers, with 9.9.

Just like the Ford 150 and GM 1500 were born when pollution controls and safety regulations were relaxed for Commercial trucks, what defined Commercial was above 1/2 Ton, so they made them just a little bit more than a 1/2 Ton.
In 1976, the quickest and fastest US made vehicle was the Dodge little red express truck, due to relaxed emissions standards for it.
Sad day.

Sorry, 1978
http://www.dodgeconnection.com/LilRedInfo.html

[Bruce K]

I went through the same thought process before buying my Suzi 15 4st. Why not buy the 20hp?, same weight etc. Talked to my insurance company, 15hp is max power for my quintrex 350 and insurance will not cover both property or personal for "overpowered" dinghy; even though the 15 and 20 are the same motor.(Only difference is an intake restrictor and CPU) This little Suzi is I think the best O/B I have owned, only problem is the slight vibration sends my throttle hand to sleep!!

[Uncle Bob]

Originally Posted by Bruce K

I went through the same thought process before buying my Suzi 15 4st. Why not buy the 20hp?, same weight etc. Talked to my insurance company, 15hp is max power for my quintrex 350 and insurance will not cover both property or personal for "overpowered" dinghy; even though the 15 and 20 are the same motor.(Only difference is an intake restrictor and CPU) This little Suzi is I think the best O/B I have owned, only problem is the slight vibration sends my throttle hand to sleep!!

The beauty of that is a good outboard mechanic can turn the 15 into a 20 with no external indication at all.

[Navicula]

I just bought the 20hp yamaha.....had an 8hp 2 stoke,,,,great engine on an aluminum fishing boat, but on a rib it was a dog in the currents of the bahamas,....dont get me wrong with just my wife and I it was fast....throw in 5 gals of water and some beer and food it would not plain worth ****.... we may travel 7 to 15 miles by dinghy....with the 2 stroke I would carry 5 gallons of gas on board and I was always looking for fuel and oil.....with the 20hp 4 stroke I will cut the tank back to 3 gals which will reduce the weight and still do the distance but wont need the oil....for longer passages we put the engine on the rail so we also have a engine lift to go along with it.....

[fursoc]

Originally Posted by Bruce K

I went through the same thought process before buying my Suzi 15 4st. Why not buy the 20hp?, same weight etc. Talked to my insurance company, 15hp is max power for my quintrex 350 and insurance will not cover both property or personal for "overpowered" dinghy; even though the 15 and 20 are the same motor.(Only difference is an intake restrictor and CPU) This little Suzi is I think the best O/B I have owned, only problem is the slight vibration sends my throttle hand to sleep!!

Yeah, hadn’t really considered insurance. I wonder if it can be insured at all since it is home built. I’ll have to check. Thanks.

[a64pilot]

Originally Posted by Uncle Bob

The beauty of that is a good outboard mechanic can turn the 15 into a 20 with no external indication at all.

Price that computer and you’ll know why people don’t buy the 150 HP Verado and a 225 HP computer.
Same for the little Suzuki’s, much cheaper to buy the 20 HP than a 15 and a 20 HP computer.

[fursoc]

Originally Posted by a64pilot

Price that computer and you’ll know why people don’t buy the 150 HP Verado and a 225 HP computer.
Same for the little Suzuki’s, much cheaper to buy the 20 HP than a 15 and a 20 HP computer.

Would be better to get a 20HP motor and a 15HP sticker.

[a64pilot]

Originally Posted by fursoc

Would be better to get a 20HP motor and a 15HP sticker.

I actually have an 8 HP sticker on mine, in an attempt to keep it from growing legs, who want to steal an 8?
Anyway the data plate on the transom mount still says DF20A though, so Insurence wise, they want the model and serial number of course.

[Bruce K]

Originally Posted by Uncle Bob

The beauty of that is a good outboard mechanic can turn the 15 into a 20 with no external indication at all.

I actually priced doing just that, the new CPU was some totally ludicrous price, can't remember actual, but something like $800. Mechanic told me that the smaller motors actually cost more to produce than the larger, because of the inlet restrictors which are absent on the 20hp!!

[Bruce K]

Also remember that the extra 5hp is only in the last few degrees of the twist of the throttle!! Torque etc is the same, from memory the 20hp Suzi revs 500rpm faster than the 9.9.

[CaptainJohn49]

I have a 9.5 Achilles with an air floor. I use a Honda 2.9 hp because it’s light and sips gas. I store it on a drop down motorboard on the transom of my Flicka 20 . Even though it’s a short shaft I think I could use it in a bay or marina should my Yamar fail me. Emergency only of course.

Of course there are two schools of though. One is the tender is a utility vehicle and the other is the tender is a multipurpose boat for fun and transport. Don’t worry I thought the same thing. I could and almost did buy a Honda 9.9 hp since I could hang it on my Achilles but in the end the light weight of the 2.9 won out.

Just my 2 cents worth.

[a64pilot]

Originally Posted by Bruce K

Also remember that the extra 5hp is only in the last few degrees of the twist of the throttle!! Torque etc is the same, from memory the 20hp Suzi revs 500rpm faster than the 9.9.

Yes, the utility of the bigger motor is to get onto plane, it just gets onto plane, without everyone having to shift or lean forward etc. of course once on plane, you back off, or almost all do, then the 20 is no different than the 15, cause your not exceeding 15 anyway.

My AB compared to my old dink, is a dog, only runs 20 kts wide open at 5800 RPM, back way off to 5,000 RPM and it honestly is at 19 Kts.
So why would anyone ever run it wide open and only gain 1 kt, but burn way more fuel and make way more noise?

[P3sailor]

The problem with 4-strokes is the weight, it would be comparable to having another person in the back of your dink, which if not loaded properly would affect planing and most of all safety. You can always change props but what you gain at one end you sacrifice on the other. As others have stated, I would consider electric. These motors are getting better all the time and can have a considerable amount of thrust. The issue there would be the size and weight of the battery/batteries being used. I'm not aware of too many 4-stroke motors being offered in the under 20 h.p. range, I'm curious what many Australians are using?

[fatherchronica]

We have a 5hp Lehr for our nesting 12' dinghy. It always gets us there. I do not it would tow things too well, but we have moved heavy boats cruisers with it. We did it for the weight. We like being able to have 1lb propane bottles in plastic bags as backups in case I over estimate our fuel capacity.

[tomtriad]

I notice that the total payload for your intended dinghy is 700 lbs; since you seem to be interested mostly in performance, be advised that keeping the weight down is critical, and a 100 lb motor is a good chunk of your capacity.
Weight is the kiss of death for multihulls, and if you're interested in sailing your cruising cat, the best place to save it is from the stern - hanging a 200 lb dinghy with a 100 lb motor on the davits will definitely impede your progress.

I would use a smaller 2 stroke (that you can still buy new) which would be lighter, more powerful, easier to stow, and result in better performance for both your dink and your 12m cruising cat. Don't sweat the maintenance down the road - the 2 strokes are simpler and more reliable; I have a 20 year old Mercury 3.2 on my 10' Achilles and have no problem getting parts for it. It weighs 28 lbs., about half the weight of 3 hp 4 stroke, and it will plane the dink with me and my wife in it.


I also note that very few of the replies are from those who have actually used a catamaran dinghy. I have a pal who built a small (10') plywood one, and who powers it with a 6 hp 2 stroke Suzuki - it planes out with 2 adults on board and is light and economical to use. My friend's little cat dink will easily do 10 knots because it is low drag and doesn't weigh down the stern; as soon as you start towing someone in the water your performance will drop and it's unlikely you will plane even with a 20 on it.

I suggest you contact Sberg, who has one of these dinks and can speak from experience - maybe get a test ride.