Best Outboards for Displacement Craft?

Anyone have suggestions on the best outboards for a displacement catamaran that has the following specs:

Length overall: 44'-10" (13.67 m)
Beam: 25'-0" (7.62 m)
Draft: 1'-9"/6'-3" (0.53/1/90 m)
Weight: 11.900 lb (5.398 kg)
Max Displacement: 18.292 lb (8.315 kg)

The pickings look pretty slim out there.

 

I did a little poking around and found this discussion of the problem. Food for thought.

http://cruising.stuffiminto.com/mul...l-outboard-engines-cruising-catamaran-15.html

post #148.

 

Wow, Hoyt.

You know how to lock into a topic. That was a good post I had read once and forgotten. Trouble is, I don't think they have a Honda 45 these days with long shaft 3:1 (or so), gear ratio and large diameter prop.

I'll take a look around to see about the new Honda lineup. I think all they had was a 60 with poor gear ratios.

 

http://dadsjunk.usedvictoria.com/classified-ad/45-HP-Honda-4-stroke-long-shaft_14615872

 

They have a 2011 40 hp 4-stroke with a 2.08/1 gear ratio.. then it jumps to 50 hp. Don't know the props available.

 

Mercury has "Big Foot" models of their 40 HP, 50 HP and 60 HP 4-stroke engines. Larger prop and gear case than the regular models. http://www.mercurymarine.com/engines/outboards/fourstrokes/40-60/?model=3

Yamaha has "High Thrust" 4-stour models from 9.9 HP to 60 HP. http://www.yamaha-motor.com/outboard/products/subcathome/4/home.aspx

Honda has a 60 HP "Power Thrust Model". http://marine.honda.com/Products/modeldetail/BFP60

 

DCockey,
Those are just pretenders. My 40hp E Tech has a 2.67-1 gear clearly well below all those on your post. I put the next lower pitch prop on it and it still seems to go very fast so a lower pitched 4 blade prop would have considerably more thrust than that. I've got it on a big 16' open skiff (Crestliner) and while doing a bit of freighting filled the boat up w boxes of canned stuff assuming it was going to be a slow trip down the bay but it went right up on plane without a struggle. I think the prop dia is almost 14". Running light fuel burn is very close to 1.5 gph. All 40, 50, and 60hp E-tecs have this same lower unit and gear ratio. Not a special model. A unique feature of the engine is it's rpm control at low speeds as in around docks ect. Small amounts of throttle results in even smaller amounts of rpm and thrust. It's the most controllable OB I've ever run at slow speeds. I real;ly like that feature. Suzuki's also have lower gear ratios than Yamaha, Mercury and Honda. Suzuki's and E-Tech's have higher thrust engines than the "high thrust" models of other manufacturers.

 

Wow, good post, Easy Rider. Thank you for bringing the Suzuki thought into the equation.

I'm wondering what hull speed I'm shooting for, since all of these "high thrust" outboards work at certain speeds.

Is it possible they will work better on my 45' catamaran than expected, since she's a very fast and light boat?

I mean I wonder what speed I'd get out of a pair of decent outboards... The boat can do 20 knots in a lot of wind, but how easily do the hulls go through the water when motoring in comparison?

 

Mercury Big Foot is a great pusher. I'd consider a couple of 9.9's but larger would likely be more appropriate. Long shaft a must.

-Tom

 

check out with your independent outboard shop ..my local very good technically guy cursed Suzuki as he had had a load of problem motors brought in ...I personally had a lot of Suzuki problems on cars and some of the outboards are car engines turned on end ....F10 horrible

 

I don't think anyone's making bad outboards. I bought the E-Tech mostly because it is not as complicated as the 4 strokes. My Suzuki is very high tech but it's heavy and has a throttle that's not very user friendly. I remember when Suzuki went to 4 stroke on motorcycles they retained the more expensive built up crank when all the others had T bone cranks. I loved the 2 valve built up crank engine and when they came out w a new engine it had the T bone crank like a car and the other motorcycles. I was stand-offish but when I rode one I liked it. I thought the 4 valves would only be of benefit at really high rpm but it had more power even at the bottom end. One tends to like the things one has experience with. I had lots of Suzuki 2 stroke motorcycles ...250cc to 750. Loved them all. I had a 25hp Suzuki OB w a sand cast powerhead. Only one I'd ever seen. All said it was superior to die cast. Anyway I've had lots of Suzuki stuff and lean heavily in that direction but one could have the opposite experience and prefer Honda's. I think Suzuki's are better but that's opinion. In this discussion I only draw attention to the lower gear ratios and bigger propellers that are in the interest of the poster. We all know bigger slower turning propellers produce more thrust and Evinrude and Suzuki are superior in this respect. Independent shops are mostly all full of product hype and strong opinions so I go light on that. But a lot of stuff has been sold on strong opinions and hype.

 

Check into Tohatsu motors, they are great, cheap, and last forever.

 

Tohatsu motors are great. I used to have one.

I guess what I was looking for is if someone knew what outboard would be best taking the hull data into account. Hint: the answer is not a brand. It is a horse power, gear ratio and propeller pitch.

 

Don't leave out the prop diameter and blade area.

I had a pair of High Thrust Yamaha 4 cycle 9.9's on my MacGregor 36 and they were awesome. If I remember correctly they threw 13" large area (elephant ear) blade props.

If Honda makes a similar unit I would't hesitate to go that route either, they are consistantly way in front in CSI.

What mounting configuration are you using? curious.

Steve

 

CatBuilder: Given those specs on the boat, I'd think you'd be looking at:
A pair of 20 hp outboards if you just need them for getting in and out of marinas (3.5 kW/t),
A pair of 30s if you want the ability to motor at six to eight knots in calm weather (5 kW/t),
And I'd consider going as high as twin 50s if you want to be able to get off a nasty lee shore under power (9 kW/t). This would probably push you to over 10 knots under power, but in all cases your cruising speed under power will be about six or seven knots if you want decent range.
Outboards don't tend to do very well at full throttle- their life expectancy is reduced, fuel consumption goes up, and even the best of them get pretty noisy. I like to assume about 1/2 to 2/3 of full power will be used in typical conditions; the last few horses are nice to have on occasion but you'll regret it if you under-power and then need to run WOT all the time.
Whatever you choose, go with the largest gear reduction you can find, swinging the largest diameter prop it'll take, and use that as the starting point for your prop calculations.