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Old 28-07-2006, 09:52   #16
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I'm leaning tword the 40hp's on this one. First off I take it you're in GB. Arn't the currents and tides there huge? Second, a 115A alternator is going to require 10-12 hp to drive it at full load. Now add refridgeration or a water maker and you're back down to 20hp useable.
Also, the HP figures are for a new broken in engine. What HP will you be delivering to the prop in 5 years? 7 years? 10 years?. Volvo's typicly last a long time and can be great units if you can stomach the parts prices.
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Old 28-07-2006, 10:07   #17
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"...need the extra power avoid getting stopped by headseas" - which the Autoprop (with its self pitching) is effectivly supposed to give you..
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Old 28-07-2006, 10:16   #18
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NM - yes currents and tides can be fun. But as far as I understand, the flat water difference in speed is only about 1/2 knot (between 20 and 30HP). Yes that may mean missing a tidle gate, but thinking in that direction leads one to a mobo.

Fair comment on alternator: I guess it would not be at full load for too long (before batteries are charged).

I guess the 30Hp look the best compromise.

yes I am aware of Volvo parts prices.

probably the comments on saildrives in general, and Volvo s/d in particular, should be another thread......
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Old 31-07-2006, 16:08   #19
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My experience is in monohlls, however I think the details aer loosely transferrable.

In my experience, the only "good" reason for spec'ing towards the low end of the power range is to save weight on a out-and-out racing boat.

To me it is vital that your engine is capable of moving your boat to windward in a good blow, in a decent sized sea, against a current.

I have sailed on a 40' racing yacht which had a 19hp engine, and a 2 blade feathring prop and it really was not big enough (it was fast under sail though ). I have a 30hp volvo in my 40' monohull (14,000lb displacement), and frankly, that is only just big enough.

Personally, I think that the 2x30hps sound like a reasonable compromise. Sure, the extra hit to the back pocket is gonna sting, but if you ever find yourself dragging anchor on a lee shore in a blow, you will potentially save yourself a helluva lot more!
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Old 31-07-2006, 16:40   #20
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I would not get high output alternators. Go with the standard alternators and find some other means of generating electricity. The dollars (x2) are better spent elsewhere (solar, wind, genset). Get an efficeint watermaker (Spectra). Get efficeint refrigeration (Danfoss 12v based system). It's nor really necessary to attach a whole lot of "stuff" to your engines. Using your $20k + engines to do something a 1k device can do, often more effceintly doesn't make a whole lot of sense to me. Especially if it means going from a $20k option to a $25k option.

I spend 90% of my motoring time on one engine. Of that 90%, I spend 99% of that at 3/4 or less throttle. It is nice to have the extra horses, but there was only one time I needed them, and I should have been anchored that time! (can you say user error!? ;-)

For comparison, your cat is significantly lighter than mine (I am aprx. 18,000 lbs loaded). I have twin 29 hp Yanmar 3YM30's. Your cat will sail better than mine, your hull is a little narrower. If you don't OVERLOAD yours, (mine is slightly overloaded) you will have a wonderfully handling, well powered cat at 30 or so. If I were in the 45 foot range, I wouldn't hesitate to go with 40's. But twin 60 horse for a 38 foot, light displacement boat is... a lot! 80 is even mor of... a lot!
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Old 01-08-2006, 02:34   #21
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I guess it boills down to if I beleive the 20HP units + Autoprop give enough 'push' in a head wind, compared to 30HP with standard/folding prop.

Anybody with such experience?

The 115A alternators are Volvo standard fit, by the way
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Old 01-08-2006, 14:55   #22
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My guess is that 30hp might give you better resale, if that's any concern at all.
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Old 01-08-2006, 20:20   #23
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Good old American saying here...
"Theres no replacement for displacment"
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Old 02-08-2006, 10:43   #24
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For what its worth; I have a 38' Prout catamaran, 7.5 tons displacement. 2 Volvo 28 hp sail drives, now 12 years old, fixed 3 blade props, raw water cooled.

Loaded with everything for a 6 month cruise, she does 6.3 knots at 2,200 RPM in still water, consumes ~1.3 gph total (0.65 per engine). Consumes <1 gph motor-sailing, and <0.5 if idling both engines to charge batteries. If trying to make a bridge opening on the ICW or dodge a tanker at sea, she gets 8 to 8.5 knots at 3,000 rpm. Never run her there long enough to calculate fuel consumption. (Note, these are U.S. gallons)

Only problems with sail drives is cooling water inlet got small muscles moving in and caused overheating. Only way to get them out is to disassemble. I put in through hulls and sea strainers directly feeding cooling water to the engine to solve the problem.

Based on this, IMHO 30 will be plenty of HP unless you’re going to spend a lot of time motoring upstream.

This boat is South African built, has crossed the Atlantic 3 times, and is pretty heavy (out weighs many longer, wider cats).

If interested see more about her at the web site listed in my profile.

George
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Old 02-08-2006, 10:57   #25
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Thanks SSB. What is your cruising speed on one engine?
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Old 02-08-2006, 11:20   #26
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In still water, ~ 5 knots at 2,200 rpm. Seldom cruise on one engine. Frequenlty motor sail on one engine just becuase it keeps the batteries up.

Motoring on one engine is easy. Docking bow in on one engine doable. Backing into a slip on one engine, nightmare.

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Old 02-08-2006, 17:58   #27
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My 3.2 liter turbocharged engines generated 422 rear wheel horse power last time I had it Dyno'd, It is spec'd to do 184 peak. I had it up to 165 or so at Watkins Glen a few years back. In the hands of a knowledgable driver there weren't any Vipers or Corvettes that could keep up with it. There were other Porsches that were faster, at pretty much the same displacement.

Truth is, it is not ALL about displacement. There SO many other issues, cost, weight, maintainability, resale to name just a few. One major fact is we are not talking about planning or semi-planing hulls. This is a displacement hull, to drive this boat beyond hull speed is going to take a WHOLE lot more displacement/props/HP.

My experience pretty much parellels George's (hey! When you coming over!?) 17, is okay, but gives you very little reserve. Very econmical. 29 (3YM30's) gives you a lot to spare. ANy larger and if you won't be able to swing a big enough prop for the engine anyway. (I can only get 16" props under my cat, You'd probably need 17 or 18 to take advantage of the extra HP).

There is a site, Yanmarhelp.com. They have a link to a displacement length hp calculator. It is a relatively long process, but it would give you a good idea what is optimal. I think I came up with something like 38 HP for my cat.

Cool on the 115's stock is good? What is a spare going to cost you? I'd get a spare alternator and spare starter. Save you some frustrations, maybe.

Cheers,

Keith
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Old 02-08-2006, 18:58   #28
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Kieth,
I disagree with carrying large expensive electrical spares on an ocean boat. By the time you'll need them they'll be useless paperweights. On nearly every island there is someone who has the brushes and parts to rebuild them. Besides on a cat you already carry a spare. Just install a paralell switch to the battery banks and canabalize the non dominant engine untill you find civilization again.

P.S. in the right hands on the right track my old supercharged Miata would run with your P-car. Were talking about forced induction here. Take the 3.2L and multiply it by the S.C.C.A. factor of 1.3 (I think) and you efectivly get a 4.2L. Turbos are just free displacement for gas or diesel
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Old 02-08-2006, 22:00   #29
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Pat;


Hmmm.... Let me tell you a couple of stories about 2 sailors in the Bahamas, oh, 3 months ago. Well the first sailor, let's call him Scott. The pinion gear on his starter sheared off. He removed the starter looked at weldinging it, replacing it, not much luck. After fiddling with it in Georgetown for 4 days. He decided to get another one. He ordered it. they had to fly it from the states into Nassau. From there, it was going to cost him another $120 to fly it down to Georgetown. Now, Scott, he's a frugal man. He ponders, I already spent $180 having it sent from Florida to Nassau, I don't want to spend the $$$$ to get it down here. I'll just have a friend bring it down from Nassau, heck no rush, I am having fun in Georgetown. Well, the friend brought it as far down as Staniel Cay. The friend said he had to get back to the states. Well, After sitting in Georgetown an extra week, Scott decides I think I'll have to go up a fetch it. So, Scott goes up to Staniel Cay, (sails up no less!) Get's the new starter, replaces it, back in business. Happy day, only cost him $500 (about $320 for the starter $120 shipping $30 stamp tax, $30 handling charges) and 3 extra weeks down in Georgetown. Now Scott had originally decided to go to DR and keep his boat there for Hurricane, with the time and mechanical breakdown, he turned around and went back to the states.

The other sailor, lets call him... Keith. He was sailing from Turks and Caicos back up to the Bahamas. All of a sudden Eva yells, I smell smoke! The instruments just died. Keith rushes down to the running engine space. Sure enough, there are wisp of smoke, Hmmm... Not good. Engine is still running, but no electricity. Must be the main fuse. Checks the fuse. Sure enough, it is blown. Keith, being the prudent guy he is, check the wiring, Hmmm, Starter wire is rather warm. Jumps fuse, smoke coming from the starter, Hmmm.... Eva, kill the engine! She can't, no electricity for the shutoff solenoid, No worries, I'll, oh ah, Keith, just kills the engine by pressing the manual solenoid. Removes the wire from the starter, jumpers the fues. No smoke! That's good. Keith, puts in a new fuse, very glad he bought a few extra! starts up the other engine. Vroom Back to motor sailing. Hmmm.... What's up with the starter. Keith removes said starter. Examines it, oh (explative deleted!) I did this. He thinks back to just before leaving South Caicos, I was tightening all the fitting on the starter/alternator. When he tightened the cable, it came to rest on the actuation terminal of the starter solenoid. Some time during the past 20 hours of running it wore through the shrink wrap of the terminal, shorted to the post and caused the starter to run for some n number of minutes, hours??? Well, let's see how bad it is. Hmmm... After taking it apart and seeing the brushes are slag, the commutator is burned beyond repair, he say, new armeture, burshes and carrier plate time! Well, our intrepid sailor gets into Georgetown, no big worries. Anchor, have a drink!

Over the next few days, he communes with auto repair, marine supply and of course the ever useful net. No spare starters, no spare armatures. He does run into a guy named Scott who says he has an old starter with a broken pinion gear, maybe you can use my armature? Hmmm. Big Bendix starter, little Hitachi starter, I don't think that will work! So, No worries! How much to order a starter and have it shipped here? No problem mon, just $460. OUCH, But the starters only go for $180 from the dealer, in the states. Hey, I know! Cliff and Orma are going up to Canada maybe they can bring me one back with them when they return.

Well, Cliff being the kind generous ever giving soul he is says, no problem! I'll just pick one up for you and bring it back with me! He runs into the dealer from Hades, he keeps promising the starter will there tomorrow, but we all know tomorrow is always a day away. On the day of his flight, Cliff drives down to Seattle to pick up the start, that they have guaranteed will be there that morning at 9:00 o'clock. Well 9:00 no starter. It is on the UPS truck, well find the UPS truck and get it from him. Well, at 10:30, no truck, Cliff has to go. He has a 1:30 flight. Well, the next morning, Cliff calls the dealer. Hey! Good news, the starter is here! Not good news, I am in Miami Florida. Hmmm... We'll ship the starter to you, but we don't know anything about shipping to no Bahamas! No problem, just send it, we'll take care of it down here !

Now, if you have cruised outside of the states, you know that getting things from the states can be a LOGISTICAL NIGHTMARE!!! It is NOT simple. So, Cliff gets to Georgetown and tells Keith about the starter, Keith says, ohhh... Well.... it's only going to be money and time. The next couple off days, Keith goes to the market, Any UPS, No, not here. Cliff calls dealer, gets tracking number, starter is in Nassau. Hmm, Well, calls nassau. Yes, your starter is here, but you have to pay duties, freight is owed and it cost extra to ship it down to you in Georgtown. How much is that, oh, you owe use $300 more dollars and the starter is your's. I, err Keith, says, I already paid $200 for the starter, I thought it WAS mine. Nope $75 duty $35 stamp tax, $190 for expedited shipping and if you want us to put it on a plan to Georgtown it will cost another $50. How do you get it here otherwise, On the slow mail boat that goes via china. When does the boat leave? Today, put it on the boat! Well, the next day, Keith goes to the agent. I am looking for my starter, hmmm... not here, call Georgetown. Oh, your starter is here, the boat didn't leave yesterday, it left the day before yesterday. Oh, if you want us to put it on the plane, it is only another $50. No, sigh, put it on the boat. Next week comes, the starter arrives... It is, the right one! Goes in in 10 minutes. So, what did this cost for the $180 hitachi starter that I could have gotten from a motor cycle shope for $90? I paid just around $500, not counting the cost of phone calls ($1 per minute, emails, $5 per day) and fuel running back and forth. How about the time 3 weeks in Georgetown. That was the time Keith was going to spend in Abacos.

Now, spares is a personal thing. One has to do what one thinks is best. I do carry an extra engine, and after cruising for a while, I am certainly glad I do. I have had filters clog (just once!) The starter debacle! I thought I lost an alternator once (it was just the wire needed tightening, see above ) and had the engine overheat a couple of times. Each time, it has never been threatening, I just turned on the other engine. I suppose I could have made the trip from Georgetown all the way up to North Carolina on one engine. But, it would have put a lot of stress on me knowing that the engine I had left HAD to work. Definately not worth $500 to me. It would have taken all the FUN out of my trip up through the Exumas and Abacos. It would have meant I would have gone over to the states at Cape Canaveral instead of Charelston. That would have added at least a week of time. Which would have been one week less time enjoying the Bahamas.

As for big electrical component, Starter weighs in at... 6lbs, the generator is about the same. Starters in the states cost $180 dealer retail! Alternators about $320. Both of these can be had from discount houses for about half that price, if you shop. For me, experience says, get it now. Getting stuff outside the state is OFTEN a BIG challenge. Get it cost effectively is even MORE of a challenge. We decided not to do the rest of the Caribbean because there are some critical things we did not have spare for. Like:

Extra RO membrane
Extra pump for watermaker
Extra water pressure pump
Extra starter (get armature for old starter)
Extra portable bilge pump
Extra keyboard for computer
Extra compressor for refrigeration (wouldn't recommend this for anyone else)

So it is still up to each individual capitan to decide what is best for their own boat. All I do is try to share my experiences and give folks some thing to consider that may have slipped their minds. Oh, all those spares above are for stuff that is new on the boat. Between wear and user error, it is just amazing the things that break.

I shirkwrap my spares, no issues so far. Tools are another matter!!! Wish I could shrink wrap them too, but then I couldn't use them.

A turbo charger is a type of super charger. The only differnce is what drives the compressor. "super chargers" ostensibly are driven by a belt hung off the crank. Turbo charger use "waste" exhaust gasess. A "super charger" will spool faster and give much better off the line performance. Once a turbo is spooled up it will provide the same boost as a "super charger" with no loss at the crank. Each has to be optimized for the expected run conditions to maximize performance.

I believe the only place a miata would stand a chance against a 930 turbo Porsche is at an autocross. Those courses are very short, narrow and twisty. If the supercharger is dialed in, and the suspension is tweaked and new brakes are put in, I would not bet against the Miata. Heck, I wouldn't bet against a mini-Cooper. But on any road track, a miata would be toast. I have only done 3 drivers ed events at tracks (twice at Laguna Seca, once at Watkins Glen) I would be willing to drive against ANY driver in a miata at either of those courses.

So, never monday, if I understand you correctly a supercharger is a substitue for displacement? The multipier has been used by many different racing bodies to try to equalize the advantage presented by turbocharging. It is only one of MANY factors that contributes to the run class of a particular auto. IF you look at the SCCA rules (I used to be a tech inspector for autocrosses in Riverside, back in my youth Even raced formula Vs) most of the known/standard autos are given a particular class and only those vehicles really compete against one another. In the X class, which is as close to unlimitted as it gets, I think there are two categories, above and below 3.0L. There a turbocharger requires a multiplier of the displacement to arrive at the proper class. But, if we want to discuss this further, we should go over to Rennlist.com.
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Old 03-08-2006, 03:28   #30
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Hmm. Some folks sail without an engine at all.
Most monohull sailors go with sail, plus engine, plus spares
The cats I am looking at have sails, plus 2 engines, and I would expect them to provide redundancy (ie I can run Ok on one engine) - so in effect I would have hot standby.

I beleive that is sufficient. (OK, plus also spare impellors and light cheap items)

Granted one could carry spares, and spares for the spares etc, but I dont think I will. There are enough spares to carry for non-redundant items
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