Double Outboards on a Catamaran

[smj]

Originally Posted by Boatguy30

AJ,

I was going to ask how he liked the Suzuki’s until I read his entire post.

The Vardo will go as well as he suggests with the Single T8 and 5 3/4” pitch prop.

I like the idea of the Suzuki being fuel injected

[smj]

Originally Posted by sailjumanji

The FP L37 is a nice boat, but I also would think a little heavy for twin 9.9s. Even the Yamaha high thrust versions. My Seawind 1160 Lite (38 ft) came standard with twin 20 hp Hondas, but we went with optional Yamaha 25 HTs.

The FP Louisiane should do well with the Yamaha 9.9’s as it weighs in at less than 7000 lbs?

[Bunji]

Originally Posted by jeffscott

I have a Fountaine Pajot Louisiane 37 with twin 9.9 Suzuki outboards. I am happy with the set up. BUT they are only useful for docking, or light wind situations. They will not power the boat against wind over 15 knots, or choppy seas.

This is where gear ratio and prop size makes a difference, pick up a 10 inch prop (honda, Suzuki, Tohatsu, Mercury) in one hand and a 12 inch prop (yamaha)in the other and then factor in gear ratio, I had 20 hp hondas and all I got after 70% throttle was prop slip.
Like rockin up to the start line with bald tyres

[Franziska]

Hi, I get all this, but have a few thoughts from a practical standpoint.

1)
Standart props for the Yamaha 9.9 high torque engines. As these engines are specifically made to push larger boats at slower speeds through the water, I would think they deliver those outboards from the factory with suitable props for this purpose.

2)
Testing different prop setups, I'd love to test, but buying several just to get the right one seems not practical.
I'm in Europe, but have not heard of any shop with sufficient props close to the sea which allow you to test (in our case it would be interesting to see what a difference another prop would do on our dinghy with its small Suzuki).
I am aware that you can narrow the choices by calculating the right prop, but, testing seems way better.

3)
Choice of props. There is not really a big choice of props fitting to the Yamaha 9.9 or the small 4hp Suzukis, is there?

So in conclusion in reality most of us are stuck with what comes with the engine, no?

[Bunji]

Originally Posted by Franziska

Hi, I get all this, but have a few thoughts from a practical standpoint.

1)
Standart props for the Yamaha 9.9 high torque engines. As these engines are specifically made to push larger boats at slower speeds through the water, I would think they deliver those outboards from the factory with suitable props for this purpose.

2)
Testing different prop setups, I'd love to test, but buying several just to get the right one seems not practical.
I'm in Europe, but have not heard of any shop with sufficient props close to the sea which allow you to test (in our case it would be interesting to see what a difference another prop would do on our dinghy with its small Suzuki).
I am aware that you can narrow the choices by calculating the right prop, but, testing seems way better.

3)
Choice of props. There is not really a big choice of props fitting to the Yamaha 9.9 or the small 4hp Suzukis, is there?

So in conclusion in reality most of us are stuck with what comes with the engine, no?

"m

Choices are limited in smaller hp, Dealer will supply motor (new) with your choice of prop. Honda has only 1 10x7 what they call a high thrust prop (4 blade) Yamaha has 3, 12x53/4, 12x7, 12x91/4, haven’t looked but yes Im guessing there is no choice with 4 hp Suzuki, probably need more hp for your dinghy

[Boatguy30]

The EFI is great until you need that Suzuki shop at Minerva reef or many other 3rd world spots. I have a complete set of electronics, a complete head and spare carbs for the Yamaha

[Franziska]

Thanks, our Suzuki is an over 20year old 2 stroke, without complicated electronics. We got it from a freshwater lake where it had hardly been used.

Regarding the Yamaha your are right, it's good to have those spares.Still we have two of them so we may get by with one in a squeeze..

Originally Posted by Boatguy30

The EFI is great until you need that Suzuki shop at Minerva reef or many other 3rd world spots. I have a complete set of electronics, a complete head and spare carbs for the Yamaha

[44'cruisingcat]

Originally Posted by Bunji

"m

Choices are limited in smaller hp, Dealer will supply motor (new) with your choice of prop. Honda has only 1 10x7 what they call a high thrust prop (4 blade) Yamaha has 3, 12x53/4, 12x7, 12x91/4, haven’t looked but yes Im guessing there is no choice with 4 hp Suzuki, probably need more hp for your dinghy

Honda has 10x6 3/4 and 10 x 7 5/8 high thrust props.

Some dealers are selling Solus 10 x 7 props as Honda high thrust props. These are nowhere near as good as genuine Honda props.

[CMNZ]

I have a question that does not seem to have been specifically answered in this topic and I have searched the forum and haven't been able to find an answer elsewhere either.

The two options for twin outboard sailing cats below 12m seem to be 9.9hp or 25hp and as far as I can see similair sized boats seem to use both equally. I understand that these two choices are because they are specifically specc'd with extended shafts and high thrust props (certainly in the Yamaha lineup) but what I cannot figure out is why they do not appear, from the posts I have read, to have an awful lot of difference in performance.

Am I wrong in this last observation and if so how wrong? Not really understanding how HP affects performance in an outboard I would have expected that a 25hp engine should provide significantly higher performance (2.5×?) than a 9.9HP.

I am building an 11.6m (38') Simpson sailing cat that will likely displace a max of 5500kg (12k lbs) fully loaded when finished and I need to decide which engines to use.

Would appreciate some enlightenment.

[Rumrace]

Monohull Owner so no Cat opinion
I would say my Favourite 9.9 is YAmaha and the alternator is not designed to charge a house bank.
Diesel lawn motor engines are more efficient because of Torque and fuel density vs power. Diesel may suck but until electric and hydrogen pass it, it’s your best bet long range fuel. Darn it.
Your transom is not like designed to push a boat. Even a roll up Dinghy has a solid transom to push.
Hope you make great memories with the children. Sounds fun.

[Rumrace]

I have a newish 40hp Yanmar. It’s kinda putting out 40hp around 2100 RPM from there to 3,000 rpm the motor doesn’t do much cause of hull speed. A Cat with its daggers up motoring I imagine has a pretty good hull speed. A pair of 29 Yanmar with Sea Drives would cost less than two Yamaha 25hp which reach their peak HP above 4,000 RPM. About $3,000 more. Fuel density would require bigger tanks for the gas option than the diesel killing your space saving theory.
Also the crappy alternator the Yanmar comes with is for a boat to charge a house bank of sorts.
You could blow the bundle put in two 5,000 psi hydrogen fuel cells and Yanmar pending little H2 motor. Toyota is finally producing hydrogen on board a Cat using salt water intake as generator. Japan settling up shore line hydrogen plants. Stored super cold in liquid then gases off specific pressure to system. US has a format goal for hydrogen cars with a range of 300 miles. Boats in salt water have an edge parked in a conductor in generating electricity. Now that Toyota Yamaha and Yanmar are producing hydrogen on board with excess energy consumption and pollution leave the conversation.

[fourlyons]

Originally Posted by CMNZ

I have a question that does not seem to have been specifically answered in this topic and I have searched the forum and haven't been able to find an answer elsewhere either.

The two options for twin outboard sailing cats below 12m seem to be 9.9hp or 25hp and as far as I can see similair sized boats seem to use both equally. I understand that these two choices are because they are specifically specc'd with extended shafts and high thrust props (certainly in the Yamaha lineup) but what I cannot figure out is why they do not appear, from the posts I have read, to have an awful lot of difference in performance.

Am I wrong in this last observation and if so how wrong? Not really understanding how HP affects performance in an outboard I would have expected that a 25hp engine should provide significantly higher performance (2.5×?) than a 9.9HP.

I am building an 11.6m (38') Simpson sailing cat that will likely displace a max of 5500kg (12k lbs) fully loaded when finished and I need to decide which engines to use.

Would appreciate some enlightenment.

It is possible that the boats you are comparing where there is little improvement by going to 25hp engines, are achieving hull speed with the 9.9 motors. I suspect that would be the case with your boat.

[jeffscott]

I did better before with twin 15s and the normal 3 blade props. My boat weighs 6,500 pounds.

[jeffscott]

my 9.9s have high thrust gearing and four blade props

[smj]

Originally Posted by fourlyons

It is possible that the boats you are comparing where there is little improvement by going to 25hp engines, are achieving hull speed with the 9.9 motors. I suspect that would be the case with your boat.

Exactly. There probably isn’t enough power in either the 9.9 or 25 to get much above hull speed. I’m guessing you may get slightly better top end speeds with the 25’s, but also burn a lot more gas. The beauty of the 25’s would be the ability to achieve the same speeds as the 9.9’s at a greatly reduced rpm.