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Old 31-05-2015, 08:23   #1
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Inboard engine, hp.

Hello,
I am wondering how much HP is good enough for 30 feet ship. I think 15, 18 hp were good enough from my previous experience but not sure 9, 10 hp for ocean sailing and maneuvering in large marina area. (And in case charging battery, too.)
Thank you in advance.
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Old 31-05-2015, 12:09   #2
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Re: inbord engine, hp.

I should think that the answer would be dependent on your displacement. My old Morgan 32 displaced 11,000 lb. it had a 20 hp engine. It was adequate but I would not have minded a few more hp.

The Catalina 30 has a displacement of 10,800 lb and a 21 hp engine according to spec sheet I found although I seem to recall the latest models had upped to 30 hp.

My current boat displaces 23,000 lb with a 46 hp engine.

I would suggest finding some boats of similar displacement and see what size engine they have.


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Old 31-05-2015, 12:26   #3
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Re: inbord engine, hp.

My 31 ft medium displacement had a 17 Hp Volvo. I felt it needed more. But it reached hull speed.
My 30 ft medium displacement had a volvo MD30 (30 hp?) and I felt it was about right.
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Old 31-05-2015, 13:02   #4
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Re: inbord engine, hp.

My 31 foot yacht weighs in at 11,000 lbs and has 28hp. The reason is Moody or Marine Prjoects who built her must have done a deal with Volvo and bought a shed load of these engines. If and when we repower I will drop to a Beta 25hp.

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Old 31-05-2015, 13:54   #5
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Re: inbord engine, hp.

Most 4 stroke 20 horsepowers weigh the same as a 15. I've noticed that boats that have sterns that come out the water aren't very good with outboards. Wile ones that have water lines going all the way to the transom with good buoyancy do much better. As stated earlier displacement will help determine what size you need but I personally wouldn't go less than 20hp
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Old 31-05-2015, 15:53   #6
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Re: inbord engine, hp.

For a larger engine to give optimum performance, it will need a larger propellor than a smaller engine. Larger prop means more drag under sail and poorer sail performance.

To me an engine is an auxiliary to be used to get in and out of the slip and get me home with no/little wind. It's a sailboat, not a planing hull and I'll never pull skiers so can't see the oversized engines that many people think are de riguer these days. Currently have 27hp in our 35'/13,000# boat and couldn't envision ever needing more power. Last boat had 20hp in 32'/20,000#. Worked fine, would drive the boat to near hull speed in flat conditions and cruise all day at 5 knots sipping less than a 1/2 gallon an hour.

18hp +/- should be just fine for your boat. A smaller engine will work but won't give you a reserve to beat into headwinds and seas at a decent pace. Will work fine in light air and getting in and out of the slip, though. With our old 20hp/20,000 boat, motor sailed with the engine ticking over a little above idle to beat into head winds and seas which almost never happened. Could motor sail to about 30 degrees relative wind so actually gained ground over directly powering into the weather.
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Old 31-05-2015, 16:28   #7
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Re: inbord engine, hp.

The general guide is 3-5hp/ton (of sailboat). And I can't ever see needing more, unless one has a triple decked, wedding cake, super high windage vessel.
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Old 31-05-2015, 17:20   #8
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Re: inbord engine, hp.

I think at least two factors may count, as the bare minimum:

- displacement and shape (think: flat/fin keel vs. deep canoe/full keel),
- how the engine/boat get used (think: marina in-out, vs. heavy engine use).

I have seen 1hp / ton to be marginal and 6 hp per ton to be plenty.

At 4hp per ton our flat but long keeled boat easily reaches her hull speed when clean. There is some extra left, but not much. I think 5hp per ton could be the actual upper limit of what we could ever need.

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Old 31-05-2015, 17:29   #9
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Re: inbord engine, hp.

The boat's displacement is very light side, about 6100lbs.
So,its about 3 tons, how about 3 hp per ton, 9hp to 10hp?
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Old 31-05-2015, 17:57   #10
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Re: inbord engine, hp.

I can also add that I had a 27 foot boat with a 15 horsepower 2 stroke and it was just right. I could cruise at 4kts at half throttle and had more power to go through waves or hull speed if I needed to and wasn't fighting waves
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Old 31-05-2015, 18:45   #11
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Re: inbord engine, hp.

Eric and Susan Hiscock did their first circumnavigation in a 30 foot boat with a 4 HP inboard. Their second circumnavigation in the same boat, they upgraded to an 8 HP motor. Even with my conservative viewpoint, that is a little light, but putting 30 HP into a 30 footer is overkill. In reality, the size decision should depend on your area of sailing. If you are in an area of high currents and generally bad weather, you will need more HP. If you are going long distance cruising in the tropics, you can do well with much less. What kind of sailor are you? If you sail Sunday afternoons, and have to be to work Monday morning, then a few extra HP is a good idea. What did the boat originally come with. It was probably just fine, and doesnt need more HP. I know I have asked more questions, than given answers, but in the real world , it is up to you and your intentions and skills. Best of luck, and good sailing. _____Grant.
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Old 31-05-2015, 19:16   #12
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Re: inbord engine, hp.

Thank you, gjordan,
I sailed 470 from junior high to 18 years old and became crew for holland 1/2 ton, sailed while. I was off and on last 30 years, lives on boat back in 90's, coastal sailor at So Cal.
I was quite familiar, 30 to 34 with 15, 20hp engine, but I found boats all same make and model but different engines. One has a 20hp but price is kind of high and other 2 has 9 and 10hp. I don't know this size of engine so,,,
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Old 31-05-2015, 19:49   #13
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Re: Inboard engine, hp.

It also depends on the engine manufacturer on how much usable power that their engines produced. The SAAB diesels were real torque monsters with variable pitch props of modest HP that powered very heavy boats with a 1/3rd of the HP that was needed from other engines. The newer light weight converted tractor engines are rated at much higher HP but have to be wound very tight to produce it and then not for long periods of time. Not a new engine but the 4-107 and 4-108 Perkins derived engines were actually 35HP engines but would kick out 50HP for short periods if you ran them at unsustainable RPM. A builder of large boats trying to cut corners would advertise the engine as 50HP while more modest boats would call it a by its real 35HP.
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Old 01-06-2015, 05:39   #14
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Re: Inboard engine, hp.

Quote:
. Not a new engine but the 4-107 and 4-108 Perkins derived engines were actually 35HP engines but would kick out 50HP for short periods if you ran them at unsustainable RPM. A builder of large boats trying to cut corners would advertise the engine as 50HP while more modest boats would call it a by its real 35HP.
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Yeah, my 4-108 was rated at 51 HP @ 4000 RPM.
Max continues was 3000 RPM.
The emergency power came in quite useful a few times: Once a bridge was closing as I was going through: Firewalled the engine and missed the bridge by inches.
Another time (or two) got stuck on sandbars in the Bahamas: Full reverse power
and got loose.
Excess power can be good to have occasionally and the Perkins delivered..
(The big propellor cost me 1/2 knot of sailing speed however)
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Old 01-06-2015, 06:36   #15
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Re: Inboard engine, hp.

Oops. For some reason I read outboard instead of inboard.
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