Cat with Outboards - Performance Under Power ?

[Factor]

Originally Posted by Serrano

My Seawind 1000 has twin Yamaha 9.9s. Great motors;.

Did I notice you are selling it? - Replacing it with anything.

[Serrano]

Originally Posted by Factor

Did I notice you are selling it? - Replacing it with anything.

Well spotted, Factor . Serrano's under offer at present. Great design, the 1000 - I'll miss her. But wanted something larger for offshore work, and had opportunity to pick up a Chris White 46 MkII (Peccadillo) at an excellent price. Hope its the right decision!

[Factor]

Originally Posted by Serrano

Well spotted, Factor . Serrano's under offer at present. Great design, the 1000 - I'll miss her. But wanted something larger for offshore work, and had opportunity to pick up a Chris White 46 MkII (Peccadillo) at an excellent price. Hope its the right decision!

Bloody hell - thats a step up, I really like all of Chris whites stuff. If I had the funds I suspect I would have a Hammerhead 54 or an atlantic 57. Where is/was paccadillo based? I havent seen many Chris White boats in Australia.

I thought you were asking quite reasonable money for serrano.

[Serrano]

Originally Posted by Factor

Bloody hell - thats a step up, I really like all of Chris whites stuff. If I had the funds I suspect I would have a Hammerhead 54 or an atlantic 57. Where is/was paccadillo based? I havent seen many Chris White boats in Australia.

I thought you were asking quite reasonable money for serrano.

Peccadillo is from Port Stephens. Bringing her down to Melbourne after Xmas. Always done the east coast in a hurry; this time we're going to take a couple of weeks and see the sites

[Tropic Cat]

Originally Posted by Serrano

Well spotted, Factor . Serrano's under offer at present. Great design, the 1000 - I'll miss her. But wanted something larger for offshore work, and had opportunity to pick up a Chris White 46 MkII (Peccadillo) at an excellent price. Hope its the right decision!

A Chris White 46 could be a candidate for the ultimate cruising cat. Great boat.

I wish you years and years of fair winds and great adventures.

[sandy daugherty]

counting the few outboard powered Geminis, all of the Seawind 1000's, Maine Cat 30's, most of the PDQs (32's and 36's), and quite a few under 40' cats built in the Southern Hemisphere, there are a MAJOR number of outboard equipped catamarans.
to the best of my knowlege (I was in the business of tracking these things) there have been no gasoline fires on catamarans. So much for old school objections.

Given that you can buy four new outboard motors for the price of one small diesel, and the price of a new saildrive and installation will buy a fifth, you will find yourself several thousand dollars ahead of the game after your replace a diesel with 10,000 hours on it. Your spare parts will have cost you a fraction of the cost of the diesel, but you will have spent $1200 more on fuel.

While the outboards don't provide much electrical output, they do provide more than your solar panels and wind generator, and a Honda EU2000i portable generator will recharge you house bank in a short time, for less than the price of 2 big power-sucking alternators and brackets.

Gasoline can be found anywhere, and is relatively easier to clean up for reliable use. It will run your prime movers, your dinghy and your generator, and all three can be fed from a permanent safely installed tank or two.

Outboards move PDQs faster than the factory diesels, and more economically too, now that diesel costs more than gasoline.

Gasoline won't heat my cabin, cook my food, or heat my water, but YEMV.

The only reason I wouldn't have an outboard on a bigger cat is simple; nobody makes a 130# 20-30 hp High Thrust four stroke with the scaled-up advantages of the Yamaha 9.9, and I specifically mean 3:1 gear ratio, very large propeller, and true continuous duty 20 amp alternators.

If wishes were rainbows....

[schoonerdog]

My wife has a photo of it actually, the knot meter that is as we were underway in the ICW. You can understand I had a bit of tunnel vision at the time and was a little preoccupied. I'll see if I can find it. Mind you, I don't think we were actually going forward, but we were maintaining our place. Also if I had let the boat slip to either side of the wind I think it would have been a very different story.

Originally Posted by catty

Yer, right, 70 knots, and I grew up living in a cardboard box at the bottom of a lake. ( .....monty python?)

[Cadence]

This is probably comparing apples and oranges. My Sunrunner 31 tri with a 15 hp Honda 4 stroke would do an honest 7K at .7 gal/hr. about 75% throttle, fully loaded. Full throttle got 1/2K more. I didn't even measure the consumption since it would be folly to run that way. Great outboard the Honda 4 stoke,for what it is worth.

Two on a cat that will plane might work well. I was reaching hull speed a 7K an would not plane.

[bastonjock]

the problem with the small diesel versus 9.9 hp outboard argument is that Gas is difficult to find in the marine enviroment here in the UK

Diesel can be bought for as little as 0.50 GBpounds a liter whilst gas is 0.90 a liter

so if i could push a 26-30ft cat along on a 9.9 hp yam big foot and only consume 2 liters per hour,id put up with the hassle of finding gas
in the Uk it probably costs about 5-6k to have a diesel fitted,yet a yam bigfoot 9.9 is about 1.250.00,so on the 10k new engine argument,the smaller gas engines win

[rallard]

My cat is a home built Suncat 40 powered by twin 9.9 HT Yamaha set up as shown on attachments and as recommended by Derek Kelsall. This set up works just fine. I have seen many other arrangements with motors positioned further backward and having serious cavitation problems.
Although this boat is fairly light and hulls are easy to push through waves, it is nevertheless a 40 footer and I average 1.2 gallon/hre for both engines rev.± 2/3 @ ± 7knots. If pushed harder, consumption goes up rapidly.
Agreed once in a while the engines will cavitate a bit in head winds-shoppy waters, but it is never a severe problem.
Next spring I will experience use of Garhauer stainless steel Power Thrusters around the propellers which are advertized to increase thrust up to 22% and fuel savings up to 30% and I expect that they should also substantially decrease cavitation. Reports on experience with such devices will be appreciated.

[rallard]

Originally Posted by schoonerdog

I've actually been motoring in a PDQ in 70 knots of wind, a couple times. Not fun, but the boat managed to keep her bows to the wind.

I most certainly believe that as I experienced similar situation with my even bigger 40' cat with twin 9.9 HT Yamahas and could keep the bows in the wind. I must admit that such high winds did not last more that 15 minutes and wave did not have time to build up too high. On another hand, the cat is rigged with a large wingmast and I cannot tell if it played a role in assisting the twin outoards.

[Calculator]

Ya'll - Interesting comments. Research and experience have shown that if you have hull waterline length to beam ratio of 10 or greater, there is little effect of bow wave formation on boat speed. Add power and you will get added speed. Below this ratio of slenderness, bow wave effects mount up and you will experience the "hull speed" phenomenon where added power does little or nothing for you. It is important to note that these comments apply to displacement boats, not planing boats.

The boats in the discussions above have "nominal" Lwl/Bh values as follows: Prouts in the 35-38 foot range, 8.5; Cherokee 35, 7.9; Seawind 1000, 9.1; Suncat 40, 10.26; MaineCat 30 9.8. Suncat 40 (beautiful boat!) should be easily driven. The report on the MaineCat being non-responsive to added power makes me suspect she was overloaded...nominal displacement is 2.68 long tons or 6000 pounds.

So, if your boat is slender and lightly loaded, added power should improve performance in either speed or fuel efficiency. If it is not, well....

Cal

[Cadence]

Rallard,
Just out of curiousity, does that configuration give enough prop wash for the rudders to be effective without headway. Or are the engines steerable?

[Factor]

Originally Posted by Calculator

The boats in the discussions above have "nominal" Lwl/Bh values as follows: Prouts in the 35-38 foot range, 8.5; Cherokee 35, 7.9; Seawind 1000, 9.1; Suncat 40, 10.26; MaineCat 30 9.8. Suncat 40 (beautiful boat!) should be easily driven. The report on the MaineCat being non-responsive to added power makes me suspect she was overloaded...nominal displacement is 2.68 long tons or 6000 pounds
Cal

The 1000xl is actually 10.85 mts long - LOA and 10.4 at the waterline - but the last 250mm of the transom tend to engage on minimal sail pressure - so an effective 10.65 of waterline length, and 1.08 waterline hull beam

So dependant on the hull engagement the seawind 1000XL is nominally 9.6, usually 9.86 and at best could be 10.04 - BUt for simplicity sake its at 9.75 or thereabouts

All that is based on a drawn waterline beam of 1.08, keep it 2 cm in immersion less (by keeping it light) and the waterline beam drops to just under 1mt.

And once again the theory that longer is better prevails. Unfortunately - longer doesnt fit my berth! But all things being equal the old adage of building a 50 foot boat with 35 foot accommodations still has a lot going for it.

[Tropic Cat]

Originally Posted by Calculator

Ya'll - Interesting comments. Research and experience have shown that if you have hull waterline length to beam ratio of 10 or greater...

Cal

Where is it written that "performance" always equals speed? Outboards on cats are problematic as cavitation affects performance. Keeping them in the water in lumpy seas is probably the biggest challenge.

I see you have some experience, which model Cat do you own and what cavitation issues have you solved?