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Old 14-08-2010, 13:40   #1
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Viability of Upgraded Engines on Catamaran

Hello, I am a neophyte when it comes to the world of sailing, and I was wondering if it is possible to upgrade the engines on a catamaran to ones with a higher cruising speed. The reason I am asking is because I would like to sail to places were the wind and currents are not necessarily going in my favor. I don't want to sail along at 3 knots on a long passage because the elements aren't cooperating.

Ideas?
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Old 14-08-2010, 14:15   #2
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i have the "upgraded engines" and still only go 3-4 knots into it sometimes- I think if it really gets sloppy out there its not gonna matter how big your engines are , because your going to take a real beating and so is the boat- to the point its not worth the effort -I can motor 11-12 knots on a calm day 2-3 knots or less on a rough day into strong sea/ wind- even if i could go faster it would be too rough, so I uselly wait it out or change my corse
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Old 14-08-2010, 15:31   #3
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Originally Posted by WhataWorld! View Post
Hello, I am a neophyte when it comes to the world of sailing, and I was wondering if it is possible to upgrade the engines on a catamaran to ones with a higher cruising speed. The reason I am asking is because I would like to sail to places were the wind and currents are not necessarily going in my favor. I don't want to sail along at 3 knots on a long passage because the elements aren't cooperating.

Ideas?

People do. I had a friend who had a stock cat design stretched to add bigger engines and installed lots of extra tankage under the cabin soles (ending up with essentially a double hulled boat)... And I've seen cats retrofitted with larger engines. So, not a crazy idea.

However, some points to consider:

1) IMO, the standard power on many cruising yachts is quite generous so you may be solving a problem that you don't really have.

2) If you want to motor long distances at high speed you'll need to consider tankage.

3) The added weight of the motors and additional fuel will increase the drag and you might get into a vicious cycle where you add power and fuel to get speed and range but the load slows the boat so you need more power and fuel...

4) Even for a multihull the drag is an exponential function. Fast is expensive.

5) In calm conditions you will probably be able to go pretty quickly with low power and in windy conditions you could motor sail -- even doing the bash under power it's likely that tacking will be less horrible and not much slower.

6) I'm not convinced that running on one engine is more efficient than running on both in practice. On my boat I have kept pretty good records and have looked at the difference in fuel burn and the difference is not significant. I would not install extra big engines just so that I could cruise on a singe at speed.

My guess is that if you want to motor at 6~7 knots in a calm and motor sail at the same speed when the wind picks up the standard motors and props will do fine. But if you want to do it for a long time you may need to give some thought to extra tankage and transfer systems...

Tom
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Old 14-08-2010, 16:26   #4
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Sure its possible. What speed are you getting now? It may or may not make sense depending on a number of factors.
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Old 14-08-2010, 16:39   #5
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a couple of points
the wind is always coming from where you want to go
you just deal with it or go some where else with favorable conditions
and like Ram said going fast into the seas and wind on the nose IS NOT FUN, and it is hard on the boat. It is great way to break something. Best way there is to loose a mast!!!!!!!!!
Slow and steady is the best for the boat.
And finally if getting some where fast is your desire, buy a power boat, (I don't mean that to sound nasty).
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Old 15-08-2010, 03:05   #6
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When I read the responses to the OP, I realize this must be a hot button. Diesels on sail boats are auxiliary as opposed to primary power. As such they are almost always undersized for the vessel as larger engines are more expensive to install.

Installing more HP is common and if you are willing to spend the time to learn, it's actually easy to do. My record for pulling a diesel out of my cat is an hour per engine. As for cost, look for Kubota tractor engines. They bolt directly to marine transmissions (I'm not sure about sail drives), are reliable and are found in every country on the planet. Also, rebuilt engines are very common and are 1/3 the cost of the marine equivalent. Which means that after adding the bits that are needed for your boat, they come in at 1/2 the cost of a marine diesel.

Just a thought.
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Old 15-08-2010, 05:36   #7
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The existing engines on most cats will drive her at hull speed if you absolutely need to go that fast. Getting a cruising cat above hull speed when they are not designed as planing hulls will be extremely costly in fuel.

Ditto what Denny said, if you really need to go that fast, then a sail boat is the wrong choice.

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Old 15-08-2010, 05:47   #8
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The existing engines on most cats will drive her at hull speed if you absolutely need to go that fast.
I respectfully disagree. Try motoring your boat into 60 knot winds. You'll be lucky if you make any forward progress at all. In 5 years of ownership this has happened to me twice ...so far. The last time I actually went backwards and was forced to turn and run with the storm cell. The issue was that I was caught on a lee shore.

Our boats can not be called aerodynamic, and there are times when we need the extra power. In calm seas and calm winds our boats should motor at hull speed with just one engine. It's when things go very bad that we need the power.
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Old 15-08-2010, 12:16   #9
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I respectfully disagree. Try motoring your boat into 60 knot winds. You'll be lucky if you make any forward progress at all. In 5 years of ownership this has happened to me twice ...so far. The last time I actually went backwards and was forced to turn and run with the storm cell. The issue was that I was caught on a lee shore.
So, the question: Is it worth the extra cost (upfront, fuel, maintenance), weight, etc. for a larger engine for that .01% of the time?

Or would a long term cruiser rather take that ~250lbs of weight and money saved and carry more stores....???
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Old 15-08-2010, 12:25   #10
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So, the question: Is it worth the extra cost (upfront, fuel, maintenance), weight, etc. for a larger engine for that .01% of the time?

Or would a long term cruiser rather take that ~250lbs of weight and money saved and carry more stores....???
My apologies, I should have written a bit clearer. If you lose your boat on a lee shore when things go bad, there probably wasn't a need to carry an extra 250 lbs of anything.

I'm planning an upgrade on my engines, effectively increasing HP by around 60%, because I feel it's necessary. Your mileage may vary.
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Old 15-08-2010, 12:27   #11
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Maybe you ought to get a motor cat.
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Old 15-08-2010, 15:04   #12
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My apologies, I should have written a bit clearer. If you lose your boat on a lee shore when things go bad, there probably wasn't a need to carry an extra 250 lbs of anything.
And what if the winds are 80kts?

I'm simply trying to make the point that one can't plan for 100% of what could possibly happen. Obviously you want to cover 99.99%, I'm pointing out there is cost.

To each his own.
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Old 15-08-2010, 21:34   #13
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Maybe you ought to get a motor cat.
Apparently I'm not as much of a fair weather sailor as some in this thread. The cost is minimal where boat safety is concerned. Heck if cost was that much of a concern, I'd own a monohull
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Old 15-08-2010, 22:32   #14
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Apparently I'm not as much of a fair weather sailor as some in this thread. The cost is minimal where boat safety is concerned. Heck if cost was that much of a concern, I'd own a monohull
I think the OP is looking at a new build and I doubt that the cost of having the factory install larger engines will be very high hurdle for him. But, there will be other considerations including: weight, weight placement, space and access, and tankage. Adding bigger engines will have some cost to sailing performance and speed or range. Design is holistic. Every change effects something else. Every choice will have a cost. A designer of a production boat will have made his best guess about what compromises will work well for the intended service of the boat. An owner who's needs are different from the expected shouldn't shy away from making modifications. But, with every change there is always a trade off. I would not buy a boat from a designer I didn't trust to make good decisions. And, my experience has been that designers are surprisingly approachable. If it were me I'd call the designer and ask his opinion. Though, FWIW, it is my opinion that most cruising boats have plenty of power installed so long as the props are clean. Though the tankage is often on the small side for long range motoring. Of course, tastes vary. I know a guy who put a huge stainless steel complex on the back of a 40ish foot production cat and replaced the motors with massive turbo charged beasties and put on four bladed fixed props and then motored from New Zealand to the Islands. The boat had an interesting trim, almost no bridge deck clearance and didn't really sail at all... His boat, his choices and he seemed quite happy with the whole thing. What consenting adults do with their own boats is their own business Still, IMO, worth remembering there really is no such thing as a free lunch.

Tom
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Old 18-08-2010, 14:11   #15
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As David said, there are a few factors that may or may not make enlarging your engine practical. Allow me to be over simplistic for the sake of...not being overly boring. Basically the amount of force required to move you through water and air increases by a power of two. So, to go twice as fast you need four times as much power, to go three times as fast you need eight times more power and so on. Also, remember that these are relative speeds, that if you are motoring into a headwind of 15 knts at a speed of 5 knts you're engines are pushing you through 20 knts of frictional wind force. So if your engines can push you along at 10knts in calm, they need to be four times as powerful to make you go 5 knts in 15 knts of wind.

(YES, I know this is super duper over simplified...but the basic principle is true)

As you can see, adding larger engines is sending you down a very steep slope of diminishing returns. If you want engines powerful enough to beat into a stiff wind at a reasonable pace you're going to have to swallow a lot of inefficiency. This includes the added weight on the boat which may affect sailing performance, and higher fuel cost.

My advice is to get together with someone who knows what they are doing. Decide what sort of performance you want and discover what exactly it'd take to make that a reality. You'll probably find out that the modifications are a bit more extreme then you'd like and have to compromise or you might discover that the changes you're willing to make might not be worth it in terms of additional performance.
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