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Old 06-11-2015, 16:30   #31
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Re: are the new sail boat overpowered?

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Any of those choices will work fine but I would go for the larger engine. The bigger propellers are great provided the propeller aperture is large enough to accommodate. Those gear ratio's seem plenty low especially as these Beta engines operate at fairly low RPM (compared to Yanmar).

I have what some people would say is a little too much power: 40 Hp (yanmar), 15,000 lb boat or 375 lbs per 1 horsepower. 18" fixed pitch prop. I normally cruise at about 30% power/2,600 RPM and never (yet) more than about 50% power/3,000 RPM. The engine redlines at 3,800 RPM and would drive me nuts to operate at that speed for anything longer that a minute or two. However, having the extra power on tap for close quarter maneuvering or some very high wind situation can be a real lifesaver.

On edit: My boat motors into 30 knot winds like crazy but if I did not have the wheel house, scuba gear would be needed for the spray!

Many persons believe these engines must be operated at a high percentage (75+) of their rating in order to prevent premature failure.

I, on the other hand (along with the manufacturers of these engines) believe there is no problem running these engines continuously at lower power settings provided there is at least some propeller load placed on them.

Steve

i could also get 2,09:1 gear ratio

if 15.000 lbs, 7,5 ton 40 hp...15 ton 80 hp...lets NOT overpower it..20 ton still 80 hp..

you use 30 %of it= 13 hp -> x almost 3 times lets say 33hp...

with the autoprop the engine will be always under quite high load.


i quote 200% your idea about low rev and max power max 1 min a year i don't likea screaming diesel

what is your cruise fuel consumption?
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Old 06-11-2015, 16:54   #32
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Re: are the new sail boat overpowered?

If you are throttled back and using 30 HP from a 50 HP motor your fuel consumption will be similar or better than a 30 HP motor going full throttle.

100% quote on this...it's what i want...

@akprb whats your weight full loaded?

@bongo

yes autoprop always keep the engine under load...so also the 75 will be always underload..i just send an email to the autoprop rep and ask it's own idea about all this stories...i guess an engine running 1500 rpm is better than a 2200 rpm one, maybe for days no stop...

@roland

i agree with you in what you states, complitely.

what engine do you have? gearbox ratio? your full load weight? average cruise speed and fuel consumption?

about weight balance yes hull about 15 tons (full of fuel and water, gear, people, food,ecc) of wich about 3,5 tonn on the bottom of the hull and a pivoting swinging keel , 3 meters long, thin keel, about 4 ton,( a big sheet of iron 3 meter long, 1 large, 0,20 meters widh, and maybe another 500 kg as bulbs, but still contemplating it for space in the bilge)...so in theory i would have a very nice rightnening moment....or was thinking also about 4 meters keel...and 5 ton...

let's wait for monday and the autoprop rep's answer...

p.s. the 75 has steel engine block and steel head, same thermal expansion coefficient...so bulletproof, about the 60 i don't know...i'm too pissed off to send an email and ask for it..
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Old 06-11-2015, 16:57   #33
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Re: are the new sail boat overpowered?

I 've always used the formula of 5 hp per ton to get a displacement craft to hull speed.
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Old 06-11-2015, 17:39   #34
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Re: are the new sail boat overpowered?

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The Perkins 4-108 Maximum Intermittent Rating is 46 hp@3600 rpm. Engines should not be run at max for more than 1 hour either. You were running the gut's out of your engine
Maximum continuous Rating is 37hp @ 3000rpm for the 4-108. I run our 4-107 with 1 less hp at 2450 max. What do you suppose that hp is?
Actually the engine ran superb without smoking or using much oil. My sweet spot was about 2450-2600 with a 17" Max Prop. The fuel usage for the entire time I had the boat (still have the logbook) was about .65 gallons per hour. I believe some 4-108's were rated at 51 hp from what I've seen. I was pitched to max out about 3200 rpm if I remember right. The boat did about 8.3 knots in flat water under power.
The boat and engine is still intact today 17 years later.... I was contacted by a new buyer a couple years ago. Another anomaly about that engine (for a 4-108 ) is it never leaked oil... anywhere.
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Old 06-11-2015, 17:53   #35
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Re: Are The New Sailboats Overpowered?

As far a 3 cylinder engines, I have had and ridden 3 cylinder motorcycles, (Triumph, Yamaha, MV Agusta), and they were SMOOTH as butter, from idle to over 10,000 rpm even without balance shafts. Then again, forged aluminum pistons may be a lot different than a tractor engine's pistons/recriprocating weight. It is also possible to have a 120 degree crankshaft, (as on the bikes), or to have a 180 degree crankshaft, which, would, no doubt, VIBRATE.
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Old 06-11-2015, 17:58   #36
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Re: Are The New Sailboats Overpowered?

I thought you were talking about sail power

I have sailed two modern light 41ft performance cruisers one with a 54hp and another similar one with a 36hp. The difference is huge in what regards the RPM you need to sail at 6 or 6.5k even if the top speed of the two boats on flat water is not very different.

Against the wind with some waves however the difference is huge.

Regarding consumption and autonomy (with good sea conditions) the difference is also big providing the cruising speed is maintained at about 5.5K. The 36hp engine wastes a lot less and the autonomy is increased.

That's about the difference between to have a sailboat with an auxiliary engine and a sailboat that can almost work like a motor boat.
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Old 06-11-2015, 18:10   #37
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Re: are the new sail boat overpowered?

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i could also get 2,09:1 gear ratio

if 15.000 lbs, 7,5 ton 40 hp...15 ton 80 hp...lets NOT overpower it..20 ton still 80 hp..

you use 30 %of it= 13 hp -> x almost 3 times lets say 33hp...

with the autoprop the engine will be always under quite high load.
...
First let me say that I had an autoprop for 6 years and I had loved it, just for not getting me wrong.

The autoprop has many advantages but if the engine is on the short side of power for the boat I don't think it will be a good idea. why?

Because in what regards extreme situations when the engine is struggling to maintain the boat moving, I don't think the autoprop will be very efficient comparing with other options.

Some years ago one of the British magazines made a big test with a lot of folding propellers and one of the tests was the pulling power: the boat was tied to a dynamometer and the engine tried to pull it from the quay. I was surprised with the very weak results from autoprop, much inferior than some other brands.
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Old 06-11-2015, 18:33   #38
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Re: Are The New Sailboats Overpowered?

At one time we owned a 22,000 lb Columbia 43 (43'10") with a 50HP Perkins and when pushing into 25K headwind and a 4' chop, it was certainly NOT too much horsepower. I would have liked 65 HP but along with cost, propeller clearance was a limiting factor.
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Old 06-11-2015, 18:48   #39
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Re: are the new sail boat overpowered?

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......what is your cruise fuel consumption?
About .6 gallons per hour (measured).

A handy rule of thumb that works for any diesel engine (under a load) is 1 gallon of fuel per 20 horsepower produced.

Steve
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Old 06-11-2015, 18:48   #40
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Re: Are The New Sailboats Overpowered?

My 4-108 was rated at 51 HP @ 4000 RPM and full RPM was obtained if needed.
Max continous however was 3000.
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Old 06-11-2015, 18:52   #41
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Re: Are The New Sailboats Overpowered?

Great posts. I have a new Beneteau sense 50 at about 40,000 lbs cruise equipped with a 75 hp yanmar. Yanmar recommends running at 80-85 percent max rpm which generates about 40 hp and 2 gph with flat water cruising speed. With my 220 gallons diesel I think I can motor around the world twice.


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Old 07-11-2015, 03:04   #42
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Re: are the new sail boat overpowered?

Quote:
Originally Posted by Polux View Post
First let me say that I had an autoprop for 6 years and I had loved it, just for not getting me wrong.

The autoprop has many advantages but if the engine is on the short side of power for the boat I don't think it will be a good idea. why?

Because in what regards extreme situations when the engine is struggling to maintain the boat moving, I don't think the autoprop will be very efficient comparing with other options.

Some years ago one of the British magazines made a big test with a lot of folding propellers and one of the tests was the pulling power: the boat was tied to a dynamometer and the engine tried to pull it from the quay. I was surprised with the very weak results from autoprop, much inferior than some other brands.
Polux is spot on here. Autoprop is brilliant for keeping a load on a normal or even better, somewhat oversized engine. Would be terrible for a boat with an undersized engine.
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Old 07-11-2015, 05:23   #43
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Re: Are The New Sailboats Overpowered?

Remember all HP calculations need to take elevation into accout...just saying.

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Old 07-11-2015, 06:34   #44
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Re: Are The New Sailboats Overpowered?

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Originally Posted by Polux View Post
I thought you were talking about sail power

I have sailed two modern light 41ft performance cruisers one with a 54hp and another similar one with a 36hp. The difference is huge in what regards the RPM you need to sail at 6 or 6.5k even if the top speed of the two boats on flat water is not very different.

Against the wind with some waves however the difference is huge.

Regarding consumption and autonomy (with good sea conditions) the difference is also big providing the cruising speed is maintained at about 5.5K. The 36hp engine wastes a lot less and the autonomy is increased.

That's about the difference between to have a sailboat with an auxiliary engine and a sailboat that can almost work like a motor boat.
Very interesting...

What engine do they had? Max hp? At how many rpm? Gearbox? Prop pitch/diameter? How many rpm and fuel consumption in cruise with the 2 engine?

Well for sure i'd trust more an engine in the middle of the ocean with waves and maybe very strong wind that doesn't allow to use the sail, to motor for hours if not days no stop, maybe slow...and you need a quite big, powerful engine...

I don't think in that condition have saved 2.000 euro and die without engine would be a nice idea...

I woudl get a pool about my ordinary question LOL
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Old 07-11-2015, 06:43   #45
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Re: Are The New Sailboats Overpowered?

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Great posts. I have a new Beneteau sense 50 at about 40,000 lbs cruise equipped with a 75 hp yanmar. Yanmar recommends running at 80-85 percent max rpm which generates about 40 hp and 2 gph with flat water cruising speed. With my 220 gallons diesel I think I can motor around the world twice.


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Thanks for your post

But....220gallons /2 gph = 110 hour motoring at 5 kts (Average between flat water and waves and nosewind) is 550 n\m...about a third of a oceanic crossing... 4 days of very bad wheater in a 20 days crossing...it's not such a far idea. Or do i miss something?
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