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Old 01-06-2020, 10:00   #1
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outboard engines for 46' cat

Looking for recommendations to repower a 46' sailing cat, Newer boat to us, 46' Crowther custom. She goes great under sail with dagger boards for pointing and two 9.9 Yamaha high thrust outboards that work well about 85% of the time. They are light weight, about 95 lbs. and lift out of the water when sailing to increase speed significantly (1+ knot more speed). 5.5 knots cruising when under normal conditions with engines on, not going to win any speed records but usually ok.

Problem we learned when sailing her from Maine to Rhode Island is that higher winds significantly slow her down and she is underpowered when heading upwind. Again, no problems docking or approaching an anchorage, twin screws make it "a breeze" unless the breeze is heavy and against you - heavy winds are the issue due to windage on the hulls/cabin. Looking for recommendations on higher powered outboards to replace the 9.9s without compromising the ability to lift engines when sailing. This is a weight/thrust compromise - assume (reasonable) refitting money takes a back seat to safety, weight and performance.

Considering Tohatsu 20 hp x 2, long shaft. That takes the hp from less than 20 hp t0 40. Weight would go from 95 per engine to 115.7 according to specs. Other brands heavier by about ten pounds. Priced about $3,500 U.S.each/requires professional install for warranty. Anyone have thoughts or experience with correct engine size for a cat this size or suggestions as to brand of engines? Really appreciate any advice as I have been a diesel-monohull sailor for most of my lifetime and have less experience with outboards. Loving the boat overall. This boat cannot have always had 9.9 hp engines and seems room on the engine mounts for larger size.

Thanks for any advice,
Jimmy
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Old 01-06-2020, 10:08   #2
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Re: outboard engines for 46' cat

I'm very satified with the Tohatsu 40 and the Tohatsu 4 on each of two boats. Being four stroke really helps with reliability, and the weight is about the same as two-strokes.

Assuming the right prop for your application (top out at about 6,000 RPM), 20 HP on each side should make her do what you want, when you want it. The 9.9s do sound a little weak for a boat that size.
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Old 01-06-2020, 10:26   #3
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Re: outboard engines for 46' cat

Thank you for the confirmation on the Tohatsu. The rep at a major supply house in Connecticut, who sells may brands, told me that Tohatsu is about ten pounds lighter (each engine) than Yamaha and other brands.
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Old 01-06-2020, 10:31   #4
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Re: outboard engines for 46' cat

20hp total seems a bit light for a 46cat. 40hp total seems more in line with typical power.

We had a single 25hp on our 35ft cat and in strong headwinds, we still lost significant speed under power, so with even less HP, I'm not surprised your boat struggled.

And before someone suggests it, there are places with channels where you don't have the option to tack up a channel but still have a strong head wind.
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Old 01-06-2020, 10:37   #5
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Re: outboard engines for 46' cat

Yamaha has put out a new 25hp fuel injected high thrust that come in a 25” xl shaft. All that and weighs less than 150 lbs. it would be an absolute no brainer for me
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Old 01-06-2020, 11:00   #6
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Re: outboard engines for 46' cat

Quote:
Originally Posted by smj View Post
Yamaha has put out a new 25hp fuel injected high thrust that come in a 25” xl shaft. All that and weighs less than 150 lbs. it would be an absolute no brainer for me
+1
Absolutely what I was thinking.
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Old 01-06-2020, 13:12   #7
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Re: outboard engines for 46' cat

Quote:
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Yamaha has put out a new 25hp fuel injected high thrust that come in a 25” xl shaft. All that and weighs less than 150 lbs. it would be an absolute no brainer for me
Thank you both for the Yamaha recommendation. My current Yamahas are little but tireless and trusted.

(and with regard to tacking up channels, I agree there are times when tacking could be done theoretically but not wisely. We recently had a "bomb cyclone" nor'easter drop in while sailing Maine. Those little 9.9s not exactly cutting it into a headwind while seeking shelter. Close to gale force winds required a double reef tacking-fest to get into Rockland, Maine. Cleared the jetty and did it but far too old to place the adrenaline/ego boost over the safety of crew. Pointing a cat in heavy winds is not my favorite part of sailing -- upgrading engines this month.) Thanks again.
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Old 01-06-2020, 13:39   #8
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Re: outboard engines for 46' cat

Having just gone through all of this for my 50’ cat, the bottom line is this.

You need the largest diameter prop you can fit so get an outboard that fits the largest diameter.

Second, you need a low pitch. Like 7”-9”.

Lastly, go for way more hp. 25-30hp is needed. The lowest gear ratio you can find is good too. But by far the prop diameter is what you need to maximize. That and hp.
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Old 01-06-2020, 14:03   #9
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Re: outboard engines for 46' cat

JimmyDarci,

Welcome to the club. Several of us posting on this thread sail catamatans with outboard motors. The outboards are an excellent match for the more easily driven cats...for all the reasons you noted.

For comparison I have the Yamaha 9.9s on a 38 foot cat with 8000 lb displacement. The 9.9s are a good fit here. But for the size of your Crowther I would definitely think more than 9.9 is what I would want. And for the reasons Chotu mentioned I go directly to the Yamaha T25. I suspect you will find the fuel injection a big upgrade versus the carbureted 9.9s. Put some quality fuel filters in-line upstream of the motors and you are all set.

I could completely relate to your bomb cyclone description of coming into Rockland. Did exactly that in May of 2018. Saw some great boat speeds while sailing, but dead upwind was a struggle.

Chotu, I am glad you chimed in here with what you have learned from your adventure on this subject.
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Old 01-06-2020, 14:07   #10
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Re: outboard engines for 46' cat

Quote:
Originally Posted by Chotu View Post
Having just gone through all of this for my 50’ cat, the bottom line is this.

You need the largest diameter prop you can fit so get an outboard that fits the largest diameter.

Second, you need a low pitch. Like 7”-9”.

Lastly, go for way more hp. 25-30hp is needed. The lowest gear ratio you can find is good too. But by far the prop diameter is what you need to maximize. That and hp.
I agree.

For me the prop diameter is by far the most important factor.

The smaller diameter props don't have enough grip in the water and can't compete with the wind.
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Old 01-06-2020, 14:13   #11
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Re: outboard engines for 46' cat

The 20 Tohatsu, is it a “high thrust” motor? If not then I’d give it a pass.
Just going from the other post Yamaha 25HP apparently is offered as a high thrust motor.
Be careful of marketing that will speak of a high thrust prop, that won’t make a regular outboard into a high thrust motor, I wouldn’t be surprised at all if two 9.9 high thrust motors wouldn’t push you faster into a strong headwind than two 20 HP regular outboards with four blade high thrust props.

The Yamaha 25 looks good to me, and I like the alternator. But it seems heavy, but guess all electric start ones are.
https://yamahaoutboards.com/en-us/ho...st/high-thrust

A high thrust motor, you can’t mistake one when you look at the prop, and putting a four blade prop on a regular motor doesn’t even come close.

It seems the 25 has the same alternators as the bigger motors, and after having a fuel injected motor myself for the last four or five years, I wouldn’t have anything else.
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Old 01-06-2020, 14:19   #12
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Re: outboard engines for 46' cat

Outboards with lower gear ratio, extra long shaft spinning bigger props more slowly are the way to go. We had 9.9 Yamaha High Thrust lower range gear box on our 39ft cat and upgraded to Honda 20HP with the 4 blade hi-thurst prop but normal gear box. I was quite dissapointed with the outcome thinking twice the HP would make a difference - they were nice engines but really not a lot better than the 9.9 in terms of thrust. I would go for for the 25hp Yamaha specialist high thrust with big prop. It will likely be quite a bit more expensive than the 20HP tohatsu.
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Old 01-06-2020, 14:31   #13
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Re: outboard engines for 46' cat

Quote:
Originally Posted by a64pilot View Post
The 20 Tohatsu, is it a “high thrust” motor? If not then I’d give it a pass.
Just going from the other post Yamaha 25HP apparently is offered as a high thrust motor.
Be careful of marketing that will speak of a high thrust prop, that won’t make a regular outboard into a high thrust motor, I wouldn’t be surprised at all if two 9.9 high thrust motors wouldn’t push you faster into a strong headwind than two 20 HP regular outboards with four blade high thrust props.

The Yamaha 25 looks good to me, and I like the alternator. But it seems heavy, but guess all electric start ones are.
https://yamahaoutboards.com/en-us/ho...st/high-thrust

A high thrust motor, you can’t mistake one when you look at the prop, and putting a four blade prop on a regular motor doesn’t even come close.

It seems the 25 has the same alternators as the bigger motors, and after having a fuel injected motor myself for the last four or five years, I wouldn’t have anything else.


The Yamaha 25 with the xtra long shift appears to weigh in at 154 lbs. slightly higher than I thought but very light for a 25
Another option would be to replace one 9.9 with the 25 and keep the other 9.9 for maneuverability. The single 25hp motor should have more power and the ability to push you faster than the twin 9.9’s.
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Old 01-06-2020, 14:33   #14
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Re: outboard engines for 46' cat

You don't mention where the engines are located, rear beam, transom or pods.
Are the props on the current set sufficiently far enough down in the water. A lot of times the lack of power is actually poor grip because of cavitation near the surface.


If you decide to go bigger and heavier. Before committing add some steel/iron weights equivalent the the additional weight of the proposed engines and see how she floats.
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Old 01-06-2020, 20:13   #15
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Re: outboard engines for 46' cat

Your advice is appreciated. Knew I had to ask you guys the moment the engines failed, I hit speed of 12+ on a double reef with white knuckles gripping the main sheet ready to rip and release. That look of trying to stay calm as there is no way to safety but upwind. Yep, to the engine dealer I go. Thanks guys!
(At only 10,500 lbs, cat is still a sailing beast but needs better way to go upwind)
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