Twin engines for cruising cat

Discussion in 'Multihulls' started by SURRYEQUIP, May 31, 2016.

  1. SURRYEQUIP
    Joined: Feb 2006
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    SURRYEQUIP Junior Member

    There are a lot of different factors in selecting the engines for a mid 40's cat. How much hp? Where are we going to put them? What kind of drive? saildrive, inboard, steerable leg? If they go deep in the hull ala Maine cat when will they get serviced? If they go amidships like Antares 44 same question. If they go bridgedeck mounted how long is the drive leg and how noisy will they be? How about the tradeoff between folding props or fixed. If you take a 40 foot 10,000 lb cat with twin diesels then 25% of the weight is motor related. Anyone want to put their point into the discussion? Thanks
     
  2. catsketcher
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    catsketcher Senior Member

    The problem with this type of question is that you are going to get wildly different responses unless you tighten the design of the cat down a lot more - 40ft cats can be racers that need only a small outboard or a French block of flats that needs massive engines to move into the wind.

    Engine type and placement has to be settled pretty early as it affects hull shape. Putting them aft will allow you to use saildrives (25hp about 320 kg each) and will increase pitching offshore. In the middle will mean a long shaft but much nicer motion offshore. Going up to the bridgedeck is rarely done nowadays.

    Personally - I would avoid diesels unless dragged kicking and screaming to them by the boat's size. It used to be that 38-40 ft was a game changer and meant outboards but the Big Foot 25 and 50 Yammies mean you should be able to power big boats with outboards - much cheaper to buy, no smell inside, easy to service, lighter, much cheaper to maintain and faster under sail. I wouldn't take a diesel on my 38ft cat if you gave it to me. People cry "What about the explosive petrol?" and then go ripping around in their 15hp RIBS powered by petrol they store on their boat so the safety point of the fuel is bunkum.

    cheers

    Phil
     
  3. Steve W
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    Steve W Senior Member

    Not quite bunkum Phil as most would store their petrol in a locker on the bridgedeck where the fumes can drain away. It would be foolish to store it in the hulls. I agree on using outboards rather than diesels though for the reasons you point out, as well as much quieter and less vibration. About the only downside is battery charging.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    No the real problem is getting hot water. You get it for free with a diesel engine. There is no need to use an engine or generator in these days of cheap solar power

    As Phil says, you will have to be more specific to get useful answers. I am as biased as Phil, as I have never had a diesel engine on any of my own cruising and racing catamarans up to 35ft.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  5. Steve W
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    Steve W Senior Member

    Hot water is not a problem as it is available very easily with propane instantaneous hw heaters if you already have propane for cooking etc. I wouldn't want to have to run my engine just to generate hot water. You are right that with a good solar system you should not need a lot of engine charging. I am biased toward outboards also.
     
  6. Richard Woods
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    Richard Woods Woods Designs

    LPG instant waters heaters have not been legal on boats in Europe for years. I have been told the same is true in the USA. Certainly production boatbuilders don't fit them

    RW
     
  7. Steve W
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    Steve W Senior Member

    Actually every Gemini catamaran I have seen including mine has one installed in the head so I don't believe that they are not legal. They work very well, mine will supposedly provide 18 hours of continuous hot water from a common 20lb propane tank. Now I know some peoples comfort level with propane in boats is not as high as others but once you have committed to it for cooking you are past that. Obviously common sense is necessary when using it as a fuel and we only turn it on at the tank when we are going to cook, wash dishes or take a shower and then it is turned off at the tank. obviously you crack the hatch in the head when using the water heater. It is not a fuel for ******. I have seen the claim made a number of times on forums that these heaters are not legal in boats, on whose authority? would you please point me to the law that states this?
    When surfing the web looking at used boats in other countries I see a lot of boats in New Zealand and I think Australia with these HW heaters installed.
     
  8. catsketcher
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    catsketcher Senior Member

    Yeah Steve there are some advantages to diesels. As Richard says it would be nice to get hot water and a large alternator. I took the top off our Honda 25, got a long belt and coupled it to a car alternator mounted on the side of the engine nacelle. The belt was too loose and too long and it made a hell of a howl. The boys cried to me "Turn it off Daddy!" (they were about 8). After 15 minutes of 35 amps the wobbles got too much and the belt grabbed the alternator and chucked the lot into the 12 metre water. I didn't do it again.

    Last cruise we were absolutely fine with 400 watts of solar so I don't need a diesel. We could bake bread everyday using an electric breadmaker in the spring, early summer in Queensland. I am eyeing a propane heater but will make a special locker for it so that it (like the stove) vents straight through the bridgedeck. (Only the hose will go into the head) BTW that 400 watts of solar cost $400 so there is no real need to go diesel for the amps. I made the panel bar out of alloy tube and surf boat oars so it is nice and strong and light.

    As for petrol - I store all of mine in an aft locker (max about 80 litres - about 2-3 months worth on average cruising - Kankama sails!). I only have the single engine tank in the nacelle. I don't like the idea of building petrol tanks into the boat as much as having jerry cans I can separate form all ignition sources and throw away if needed. Diesel can be thought of differently but I probably carry less petrol than most cats with large tenders.

    Diesels also have other worries. You have to buy very expensive folding props, tanks, soundproofing, heaps more filters and lots of spares. This is about the cost of my outboard. My Yammie has let me down once when I was silly and tipped the dregs of the jerry can into the engine's tank. Fixed that myself with simple tools out on the reef and was working well within an hour of carby stripping. Friends with diesels have so much more expense during services and more problems. I have only had that single one in 16 years. Cost me nothing.

    If you want a motorboat, get diesels. If you want a smaller cat to sail well, think outboards first, faster, cheaper, more reliable and quieter.

    cheers

    Phil
     
  9. Steve W
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    Steve W Senior Member

    Yes, I like your whole program, to me there are too many negatives with diesels on multies, especially cats where folks feel the need to have two, the weight is just too much but most of all the noise and vibration is not something I want to live with, I helped a friend deliver his late model Beneteau 43 about 80 miles a while ago and you could hardly hear yourself think down below, I cant imagine trying to sleep, and this was a modern production boat, unacceptable to me. On the propane thing I think a cat provides more opportunities for a safe installation than on monohulls as most runs can kept on the bridgedeck where you can, with a bit of forethought prevent fumes from getting to the bilges. On my boat I have propane stove, fridge and HW heater, I am thinking of building a second self draining well fwd just for the HW heater. people worry about co2 for the heater but ignore the fact that the stove produces it too, you just need to vent when using it, a little common sense is obviously required, personally I am more concerned with the explosion risk so am planning on mitigating that as much as possible, the stove in the hull us the biggest issue for me. I plan on getting rid of the propane /ac fridge and replacing it with an ac/dc one with solar.

    Steve.
     
  10. aussiebushman
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    aussiebushman Innovator

    As usual, I agree with Phil and Richard, not because I'm sucking up to them, but from personal experience with inboard diesels, petrol outboards and with LPG gas heaters.

    On my 30' cat I spent most of my time fixing the bloody engine before finally putting a petrol outboard onto the stern cross beam. Petrol on board was no problem because on a cat it is no big deal to construct a self-draining locker in the cockpit.

    Maybe the rules here in OZ are different or have changed recently, but two separate cockpit lockers housing the LPG bottle and the instant gas heater were perfectly legal - as long as they were a specified distance apart. Both of these lockers also drained to the sea and the only lines into the boat were for water - not gas.

    Conversely, I would NEVER have an LPG appliance inside a hull. On the same basis, this probably rules out a LPG heater on a Tri and I guess the same applies to petrol storage.

    Alan
     
  11. Richard Woods
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    Richard Woods Woods Designs

    As always, I only speak from my experience. I wanted to fit an LPG instant heater on my Eclipse but the (UK) gas installer said he wouldn't do it as it wasn't legal on a boat. So I fitted it myself. I talked to catamaran builders in the USA last year. They fit outboards on their boats. I asked about instant gas water heaters. "We cannot fit them, customers do it themselves" was the reply

    The problem is not the LPG but the possibly always on naked pilot light. Same reason you cannot have a propane fridge on when in a RV/caravan on the road. and on a boat the laws assume that all hatches are closed at some stage

    We have found 350W solar power will run our boat, including fridge/freezer in both British Columbia and Florida/Bahamas

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. SURRYEQUIP
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    SURRYEQUIP Junior Member

    OK Let's narrow it down- 45 foot bridgedeck cruising catamaran, 4 beds, 2 heads. This came to mind after looking at the diesel install on a Mainecat 41 and the owner said it would do 6 knots. I don't think I could check the oil in it without a ladder.
     
  13. Richard Woods
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    Richard Woods Woods Designs

    Daggerboards or keels? Wheel or tiller steered?

    RW
     
  14. aussiebushman
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    aussiebushman Innovator

    Sorry Steve - didn't mean to ignore your excellent comments when posing my earlier message. You are right - just keep the fumes out of the hulls

    Alan
     

  15. Steve W
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    Steve W Senior Member

    Richard, could you elaborate on what you have for refrigeration, I have a dometic ac/propane fridge that I would like to get replace with ac/dc and run everything with solar. You must have reasonable charging from 2 outboards when underway though, on a 32 day trip a while ago we were able to run a very electrically Spartan gemini with just a single 9.9 Yamaha except for a couple of days where we had a lot of starting and shutting down where locks came in quick succession in the Trent severn waterway.
     
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