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Old 28-07-2006, 01:04   #1
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Which engine?

New boat (38ft cat, slim hulls) with standard twin 20HP, optional 30, 40HP. Which to go for? difficult to change later....

One argument: 20HP lighter, less gph, adequate performance, Autoprop would give extra power when punching into seas/headwind as it auto-pitches (and that is the only time you may need it) so spend less on Autoprop and go with smaller engine.

Other argument: 30Hp allows cruising at lower revs, better passage making on one engine, extra power for motoring into bad weather, but probably only half knot faster and extra weight/expense

Use will be blue water cruising

Any experience/thoughts?
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Old 28-07-2006, 02:50   #2
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first query would be how well does she sail to windward?
What is the weight difference between the engine choices,


I suspect (not knowing which boat), that I would choose the middle option, and would also fit autoprops.
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Old 28-07-2006, 03:07   #3
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Also remember large alternators, refer compressors, etc use HP. The larger the engine the more HP you have for the add-ons that a full time cruiser will need and put on. IMHO you can't get hurt with extra HP also diesel tankage options to correct for the higher burn rate.
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Old 28-07-2006, 04:00   #4
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Please define the engine model choices. HP rating isn't enough for me to accuratly recomend an engine. Knowing which model, might make a difference in servicability.
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Old 28-07-2006, 04:24   #5
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Engines are Volvo saildrives.
Standard fit are 115A alternators (one per engine)
Sails pretty well to weather for a mini-keel cat - points to 35deg in flat water
Engines under bunks

30HP with Autoprops has a significant cost penalty, if not really needed. And weight of course.

Thanks

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Old 28-07-2006, 05:59   #6
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My leaning would be to get the 30 horse now. Keep the standard props. It is much easier to change the props if you need them, than replace engines. Is there that much difference in overall weight between the 20 and 30 hp options? Twin 40s for a smallish cat (under 40 feet) seems a bit HIGH. 30s should drive you up to hull speed.
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Old 28-07-2006, 06:28   #7
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Thanks for opinions. Volvo omit the weight of the 30HP units, but extrapolating from the 12 and 30HP engines (weight given) I would expct about a 50lb differenec between 20 and 30HP, consumption 5.5gph versus 7gph (at same cruising speed).

£3k difference in purchase price (and I would need SOME sort of folding prop anyway)
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Old 28-07-2006, 06:33   #8
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I know we're talking two engines but isn't that consumption kind of high? My 30hp (3GM30F) uses about 1/2 gallon per hour at cruising speed about 2500 rpm.
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Old 28-07-2006, 06:47   #9
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yeh, a bit high by a factor of ten.... I meant aound 0.55 and 0.7 GPH (per engine, going by Volvo graph at 2300RPM)

Incidently, the new Volvo D1 series claims 3-4db drop in noise, and 115A alternator with electronic sensor that delivers 35A at idle and 100+A at cruising speed. That seems pretty good (if manufaturers claims can be beleived)?

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Old 28-07-2006, 07:01   #10
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Is there any way to avoid getting a saildrive? They are nothing but problems. Gunboat has stated they will never put another saildrive in one of their boats.
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Old 28-07-2006, 07:38   #11
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Hi JZK
Not without making a production cat into a semi-custom job (and ££$$). Anyway, most cats made (at this size) are saildrive-equiped. I dont think what Gunboat say has much relevance to me or my needs - they are in a different world. 'Standard' drives have their problems too.
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Old 28-07-2006, 08:11   #12
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Quote:
Originally Posted by Moby Dick
Hi JZK
Not without making a production cat into a semi-custom job (and ££$$). Anyway, most cats made (at this size) are saildrive-equiped. I dont think what Gunboat say has much relevance to me or my needs - they are in a different world. 'Standard' drives have their problems too.
I have just seen nightmare after nightmare with Saildrives. If Gunboat said the problem was the extra weight, then their point would be irrelevant. They don't like them because they are crap.
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Old 28-07-2006, 08:23   #13
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Quote:
Originally Posted by Moby Dick

Incidently, the new Volvo D1 series claims 3-4db drop in noise, and 115A alternator with electronic sensor that delivers 35A at idle and 100+A at cruising speed. That seems pretty good (if manufaturers claims can be beleived)?

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Old 28-07-2006, 08:31   #14
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Its not just weight. Gunboat have a weight v. space v. cost v. 'effectiveness' * priority relationship that is different to mine.

*effectiveness: I mean how good the solution is at the job it is intended for
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Old 28-07-2006, 08:45   #15
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Moby Dick,

I'm a monohull sailor with little experience on cats. However, I've observed them and sailed with them for many years in the Caribbean. Here's my take.

1. Cruising cats are very easily weighted down due to the necessities of cruising. This GREATLY degrades their performance, especially to windward.

2. With my 42' monohull, I've very often left cats behind in a breeze, and even beat them sailing upwind when they had both engines going in the Drake Channel.

3. More power is better, not just because of the extra stuff you hang on the engines for cruising, but because cruising cats typically are dogs to windward and in a chop, and need the extra power avoid getting stopped by headseas.

4. I would echo earlier posts re: Volvos and saildrives. Avoid them at all costs. If you choose to go with them anyway, you're forewarned.

Good luck.

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