Outboard Size for 40 ft Cat

[kmargolis3]

Hi all

i am thinking of buying a 40ft Crowther cat that needs a new home. It currently doesn't have engines but pretty stout outboard mounts

The guy selling it suggested i get two 9.9 yammi's

i was a bit concerned that this would be underpowered and was thinking more in line with twin 25's -- and run one at a time for longer cruising and both if needed for speed and control in wind/tide

any advice?

thanks

[Cotemar]

I would go with 40 hp outboards on a 40 foot cat.

[44'cruisingcat]

Originally Posted by Cotemar

I would go with 40 hp outboards on a 40 foot cat.

Lol! Good one!

What does the boat weigh?

9.9 HT Yams would likely be adequate, the 25HTs would be plenty, but they are very big and heavy engines.

[Just Another Sa]

Some 40ft cats weigh 2 tons, others 20 tons. They do not require same size outboards. With the heaviest 40ft cats you would be better off with 4 outboards rather than just 2 and still require high thrust models as well.

[sailjumanji]

I'm having a Seawind 1160 Lite catamaran built now. LOA 38 ft, displacement 14,300 lbs. Standard propulsion is twin Honda 20 hp outboards. I'm opting for twin Yamaha 25 hp high thrust outboards. For reference.

[smj]

We have a 38' cat and also a 40' cat, both about 3 tons.
The 38'er is powered with a single Honda 15, cruises at low 6's top speed low 7's. Only time I feel we need a larger motor is in strong headwinds or steep chop.
The 40'er has twin Honda 9.9's. Only powered it one time from the boatyard to the marina where it currently sits. It did an easy 7kt cruise and well over 8 at top speed.
I'm guessing the Crowther is an easily driven cat so twin 9.9 high thrust would probably be fine.


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[Dave_S]

My cat loaded for a couple of nights is about 7.25t and 48' long.

I had 2 x 25hp High Thrust Yamahas, flat out around 8 knots cruised at around 6.5

I replaced them with 2 x 40hp Hondas not sure on figures for flat out yet (can't get full throttle from the controls - longer throw on the throttle linkage), cruise at 3,500rpm at a smidge over 8.5kn. Flat out should be 5500 to 6000 rpm, best case I think around 13+ kn.

The 40's are EFI, a big factor in my decision to go up in size. They are not High Trust though but it is the smallest HP rating using the same gearbox as bigger hp motors so they will be strong enough.

The 40's are a bit lighter than the 25's and similar, if not slightly better fuel economy with a speed advantage (6.5kn to 8.5kn), I guess 60% more HP and similar fuel efficiency I am happy. Speed for speed the Hondas will be better.


None of that directly relates to your use but if I were choosing again between two sizes, I'd go with the bigger size, you will have more control in the wind and swell.

[Bean Counter]

We had a 38ft cat, 4 tonnes light ship. Originally powered by 2 9.9 Yamaha high thrust with low range gear box. 5 years later I swapped then out for 20HP Hondas with standard gearbox and 4 blade hi thrust props, for virtually no difference in performance - I was rather hoping twice the HP would give extra speed and push, did not work out that way, the low range gear box and bigger props were more beneficial than increased HP in this scenario. So for a 40ft cat I would get 20 - 25 HP with low gear and big props.

[admiralslater]

Our pdq 36 is 4.5 tons. Will do about 7.7 flat out with two yamahas . Great reverse and super when the going gets rough . There is a shockwave 38 fitted the same way. I have seen them on a 50 footer as well but don’t know how well they worked

[thinwater]

The mounting location makes a difference. On the transom they tend to go up and down, whereas farther forward they are stable. The PDQ, for example, has the engine wells far forward.

[catsketcher]

Can you post a pic of the boat - there are different types of Crowthers.

IMHO you should go the twin 25s. I have twin engines - one 9.9 and one 25. My boat sits right at the tipping point between the motors so I got a 9.9 to go with my then single 25. Then I made two new mounts.

The single 25 pushed my boat 9 knots flat out lightship. I can now get 9.9 with the 9.9. The 9.9 on its own gives me about 6-7 in a calm. The twins are really just for manouvring.

The new 9.9s are smaller than the old ones, they are 8 hp uprated whereas the old ones were 15s derated. I don't know how but I think some people rejetted the things to get 15s.

I now wish I had just gone twin 25s. I can't really switch engines when motoring and can spin around better one way than the other. I certainly wouldn't want to get in any sea or big winds with my boat and twin new 9.9s. My 25 is 15 years old and still purrs like a kitten (more like a tractor really) great engine and stellar gear box and prop. Great bite on the water but lots of people use Honda 20s too.

cheers

Phil

[danielamartindm]

Originally Posted by kmargolis3

Hi all

i am thinking of buying a 40ft Crowther cat that needs a new home. It currently doesn't have engines but pretty stout outboard mounts

The guy selling it suggested i get two 9.9 yammi's

i was a bit concerned that this would be underpowered and was thinking more in line with twin 25's -- and run one at a time for longer cruising and both if needed for speed and control in wind/tide

any advice?

thanks

I think 9.9s would likely be adequate; but even given the added weight, I would err on the side of being "overpowered." Think of it as insurance.

[valhalla360]

In calm conditions, a light fast boat won't take a lot of HP but when fighting a strong headwind, power needs can go up quick.

So a pair of 10hp will likely do fine on a calm day but fighting your way up a narrow channel against a 30kt headwind, I would want the extra HP.

As someone mentioned, at 25hp, you can get EFI. We had that on our 34' Gemini and it was great. No carb issues. Starts right up. And if you go slow, you don't lose much efficiency over a 10hp.

[Reefer.]

I own a 40’ Crowther Spindrift with a single centre-mounted high thrust Yamaha 25.
There is plenty of spare power, I just have to stay away from marinas due to the almost uncontrollable state we get ourselves in at very low speed. I am considering adding a hydraulic steering kit, but it’s just another $1000 I could spend elsewhere.
And anyway, we use the engine surprisingly little.

[alansmith]

Another factor... if the criwrher u speak of is in the PNW.... wow...just do what the previous owner did... put two of your beefiest crew on the extended transom with oar locks and oars. Helps if you play Led Zeplin or Nirvana. He he

You actually have a lot to consider. Carburetors or fuel injected? Do you want redundancy in starting? An engine that can be started with electric start and pull coard? Will the motors be fixed or can they rotated with steering linkage? Will they be on sleds mounted more forward or will they be transom hung with strong bracket that is easy to hoist and drop?

Crowthers are beautiful machines. Whatever you do keep her as light as possible. You give up some comfort on speed machines so don’t go heavy on power. Another thought... you can man handle a 10-15 hp high thrust susuki or Yamaha. You go 25 Efi Honda or Merc... forget about man handling it. A brand new fuel injected Suzuki with dual start (pull and electric) with electric tilt weighs 110 lbs and cost me $2400 last year. A 20 hp Suzuki doesn’t weigh that much more and less than 3 k. EFI are more expensive and heavier machines because of bigger engines.

You must carefully weigh (pun intended) everything you do in s multihull. I agree with all the guys about about extra power when tide and wind against you. But tide is a known factor dealt with by timing your passage. Wind will slow you down tremendously. In some situations a large cat can barely make 4 knots even with twin diesels that are 50 hp. You can’t pick a power plant that will handle all situations... it is my point. Yamaha and Suzuki make the two best high thrust engines. There is no difference in weight beteeen the 10 versus 15hp. It is a chip and nozzle. Don’t let someone blow smoke up your wazoo about high thrust.... it is the gearing ratios combined with 4 bladed props pitched to get the right rpm. Some outboard companies claim high thrust but they don’t have the low end gear setup and put on a 4 bladed prop and call it high thrust.

I went with Suzuki because it is fuel injected and has pull start and electric. Yamaha and Suzuki high thrust are excellent engines. Yamaha is carburetor technology and no pull start if electric.

The twin 10’s or 20’s will handle 90 % of all situations. Or spend 2or 3x more and handle 95% of all situations and lose performance due to extra weight and weight of extra fuel for larger engines. Welcome to the dance.