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Old 08-12-2008, 14:42   #1
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Cat with Outboards - Performance Under Power ?

Greetings from a newb seeking info. Wondering what kind of speed and gph/mpg you get with twin small outboards on a PDQ 36 or similar size boat? I read an ad for Coastal Cat 34 in a magazine that stated 15 knots at 2.75 GPH. That sounded pretty good, but hey, it's an ad. What is your real world experience?
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Old 08-12-2008, 15:27   #2
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Sounds like puffing to me.

A Stiletto 27 with 18 hp goes 11kn empty (1350 pounds) and burns ~2.5 gph. A PDQ going 7kn with 2x9.9hp (7500 pounds) will burn ~1.3 gph, and about 2.5 gph at 8kn.

However, they did not say it would use 2.57 gph at 18kn. That would be at a lower cruising speed. Even so, I doubt the figures, as it appears MUCH heavier than the Stiletto, and with more windage.

I would also worry about the props ventilating in waves - they are to far back for a displacement hull.
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Old 09-12-2008, 07:54   #3
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A Maine Cat 30 with two 8 HP outboards mounted amidships will do 7 knots on 1.5 gph. That is at about 3/4 throttle. Full throttle might get you another knot. I changed to two 9.9 HP engines and did not notice a significant difference in performance.

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Old 09-12-2008, 09:30   #4
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Thanks to both of you for the answers. I started out looking at trawlers for fuel-efficient slow cruising. It appears that a cat with outboards can do diesel trawler speeds with a couple of outboards at very good fuel usage. Yes, I know that capacities and range are not the same, but I am being drawn to the cat side of things, for many reasons. I do like the idea of outboard power. I understand gas outboards. Diesel inboards are quite beyond me.
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Old 09-12-2008, 11:30   #5
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There is an important fact being ignored here.

I had a 27 hp diesel outboard on my cat, and a chum had the 9.9 saildrive. in perfect conditions, the 9.9 was slightly faster probably cause I had a much larger fuel tank as well, and was thus significantly more heavy.

However, when the wind was howling and on the nose, the 9.9 was not up to the job, whereas mine would still push through the water.
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Old 13-12-2008, 09:42   #6
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It depends on the placement of the outboard. As the PDQ has her outboards in the cockpit just aft of the helm and well forward of the transom it's not as prone to seeing the outboards cavitate in the water as some catamarans which have their outboards at the very end of the transom. 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.
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Old 13-12-2008, 10:18   #7
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I have a 25 HP Suzuki 2 stroke Oil injected, on my 36' Prout Cat, at 75% power will burn about 1.5 Gph running at 6 Kt.
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Old 13-12-2008, 10:46   #8
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I had a 50hp Honda on our old Cherokee 35 and it would burn a little less than a gallon an hour at half throttle doing mid 6's. A.J.
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Old 14-12-2008, 02:25   #9
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Quote:
Originally Posted by schoonerdog View Post
It depends on the placement of the outboard. As the PDQ has her outboards in the cockpit just aft of the helm and well forward of the transom it's not as prone to seeing the outboards cavitate in the water as some catamarans which have their outboards at the very end of the transom. 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.
Yer, right, 70 knots, and I grew up living in a cardboard box at the bottom of a lake. ( .....monty python?)
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Old 14-12-2008, 05:06   #10
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Designers with outboard powered Cats of decent size

Schionning Designs -

Ron Given Catamaran Design, sail and power, New Zealand and Noumea

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Old 14-12-2008, 05:15   #11
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Originally Posted by schoonerdog View Post
It depends on the placement of the outboard. As the PDQ has her outboards in the cockpit just aft of the helm and well forward of the transom it's not as prone to seeing the outboards cavitate in the water as some catamarans which have their outboards at the very end of the transom. 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.
With a pair of 1GM10's and in 50 knots I couldn't keep my bows into the wind. Is the PDQ that much more aerodynamic than my much smaller Catalac?
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Old 14-12-2008, 19:12   #12
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With a pair of 1GM10's and in 50 knots I couldn't keep my bows into the wind. Is the PDQ that much more aerodynamic than my much smaller Catalac?
Might have meant 7 knots

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Old 22-12-2008, 04:01   #13
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I grew up living in a cardboard box at the bottom of a lake.
That actually explains a fair bit.
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Old 22-12-2008, 04:35   #14
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My Seawind 1000 has twin Yamaha 9.9s. Great motors; like little diesels. Always start, lots of torque, low fuel consumptiom, unless you push too hard (1.5 litres/hr up to 6 knots; better if motor sailing; 7.5-8 knots max, but fuel use goes right up). I find 15+ knots hard to believe but I''m not familiar with the Coastal Cat. But the problem is cavitation. Despite long legs, they cavitate in a short chop upwind. They still give quite good control, but this limits your speed and fuel efficiency if you have to motor upwind long distances (as I did coming back to Melbourne from Hobart with constant northerlies - no fun at 4 knots).
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Old 22-12-2008, 04:51   #15
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I find 15+ knots hard to believe but I''m not familiar with the Coastal Cat. .
Only reference I found was here

[PCW] Coastal Cat 34 -- outboard-powered catamaran


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Disclaimer: this is posted by a (power and sail) catamaran dealer.

The first Coastal Cat 34 (34' x 16') was launched a few weeks ago in New Zealand (where this cat is better known as the "Prowler".) This economical, outboard-powered cruiser (2 x 60 HP 4-cycle outboards, max speed approx. 20+ knots), will make its North American debut (with the "Coastal Cat 34" name) at the big Seattle boat show in September. As fuel prices spiral ever higher, it's highly appealing that the CC-34 cruises at just 1.25 litres per nautical mile (that's barely one-and-a-half QUARTS of fuel per mile at 17 knots). And, an oddity for those of us who remember when diesel used to be the "cheap" fuel, gas now costs appreciably less than diesel.

As the dollar continues to diminish in value, there's a question as to how long the Australian builder can hold the currently posted price: $299K, including delivery to the U.S. west coast. Especially when you consider that's about $100,000 LESS than I've been told that the new, New England-built PDQ 34 will be priced for U.S. west-coast delivery. (Note: the flybridge is standard on the PDQ, while it's an option for the CC-34...but it's not an expensive option.)

The "American version" of the CC-34 will have many upgraded items compared to the Australian version (holding tank, double-sink in galley, 110V wiring, helm-station ventilation, i-Pod-ready stereo installation, etc.)

The CC-34's web site --www.prowler.co.nz -- has been updated with some fresh photo's of the recently launched hull #1, plus a narrative about the boat's maiden voyage.

It's comforting to learn, too, that this isn't some all-new venture. Previously there was a successful 29' model that enjoyed great success. (In fact, one of those fared extremely well just a few weeks ago in one of Hawaii's big fishing tournaments, providing a stable platform and plenty of "get-there" capability in the boisterous, deep-water ocean conditions off the Hawaiin islands.)

The CC-34 coming to Seattle (hull #3) will be berthed here for at least a few weeks before and after the Sept. boat show. Reservations already are being taken for seatrials to be conducted on Puget Sound.

I'm curious to see how the aft-mounted outboards fare in short, choppy seas. Then again, this model's similar-design "little sister" has proven itself in some remarkable rough-seas situations in previous years. In like manner, cats such as the Glacier Bay 30 and 34 have demonstrated GREAT performance for long-range, offshore cruising with similarly aft-mounted outboards. So have the outboard-powered C-Dory cats, and the new Arrow-Cat 30.

Most of the power cats my company reps are diesel powered. But I'm becoming increasingly convinced that the benefits offered by the latest 4-cycle outboards make them a real (and serious) propulsion contender -- and arguably even superior to inboard diesels when used in 'pocket-cruiser' catamarans. Consider these benefits:

-- Cost less than diesels
-- Quieter & smoother running than diesels
-- Well proved (currently powering about 85%-to-90% of all power boats in use)
-- Elec.-tilt for easy beaching (this is no small thing for a pocket-cruiser -- how nice to be able to just nose up to a sandy beach, tilt up the motors, and then you and your pets or kids or grandkids can, with a small ramp or step ladder, disembark off the bow directly onto the beach, with no need to go through the whole dinghy-launch procedure)
-- Easy repair, & loaner replacement
-- More interior room for you (taking the engines out of the hulls frees up a LOT of room in a small cruiser)
-- Easier access (what a difference from other small cat-cruisers fitted with inboards, in which the engines are stuffed under berths, or crammed into narrow, hard-to-get-to bilge compartments, etc.)
-- Outboards also are superior at operating at slow, fish-trolling speeds
-- No diesel odor inside the cat, nor those noxious exterior diesel-exhaust fumes.

Alternatively, the 'plus-factors' for diesel engines?

-- Their larger alternators provide more electric/battery power. (Conversely, an outboard-powered cruiser, pursuing long-range coastal cruising, benefits from the addition of 1 or 2 solar panels.)
-- Diesel engines have a longer life than outboards (which helps justify their greater expense)

In cat-cruisers of the 32' to 36' length, price is often a more important consideration than with larger cats. As such, the cost/value/performance combination offered by the Coastal Cat 34 may make it an especially popular addition to the growing list of similarly sized cat cruisers.

Rod Gibbons
Cruising Cats USA
Seattle - Portland - San Francisco Bay - Hawaii
(206) 297-1330
They are a powercat http://www.prowler.co.nz/

Schionning make a prowler as well, may be related

Schionning Designs -

Dave
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