Motors for 40' Cruising Cat

[Tropic Cat]

I too have straight shaft Yanmars and love the motors. However, I haven't been as fortunate as some as far as performance is concerned. Taking my Cat head on into 45 knot winds is OK but 60 knot winds has killed forward speed (in many separate instances) and I most assuredly wanted for more hp. If I ever repower it will be with larger diesels and weight be damned. Safety is number 1, not another 1/4 knot of boat speed under sail.

[Nordic cat]

Originally Posted by sandy daugherty

Weight control is a constant vigil, and the much repeated phrase "it's only 32 kg more" applies to every single thing that goes aboard. For most of us, the slightly greater speed of a catamaran is a drawing point (but obviously not for all of us, Rick) and speed evaporates somewhere along about the second time you repeat that phrase. Just once in all the sailing I've done on my PDQ has 20 total horspower not been enough almost. We made it in anyway, pitching 30 degrees. I could have done smarter things.

Weight control is important, the 60 kgs extra is instead of a generator that maybe weighs 150 kgs! No need for an extra engine and all that entails in the way of auxiliary fittings.

60 kgs is also 2 extra batteries

As usual, you need to make your choices wisely, balancing all the facts with needs.

Alan

[fastcat435]

Having enough hp is important what is even more important is having enough hp available at the prop, the losses vary a lot between one manufacturer and another, losses of 25 % are not uncommon while 12 % is also possible. if you take a 40 hp engine and a 25 % loss of power that leaves you with 30, if you use a 2 blade folding racing prop ( the worst for transmission losses you might end up with only 8 hp to propel your boat.
Using a good 3 blade feathering or folding prop like ( for instance a autostream or a gori or if you like light weight a kiwi prop) decreases your losses to 60 % instead of 75 %.
My choice would be a smaller motor ( 30 hp )with less transmission losses ,a saildrive with a lower hydraudynamic resistance and a 3 blade folding or feathering prop like mentioned above and you might end up with more actual power than with the 40 hp saving some weight along the process carrying less fuel aboard and saving some money in the process
my 2 cents

[Nordic cat]

Gideon,
I'm a bit confused by your above posting, can one expect to lose 75% power by using a 2 blade folding prop compared to only 60% on a 3 bladed ?

can you point us to some verified documentation of your claims for propeller efficiencies and drive train efficiencies?

Are saildrives more hydrodynamically efficient than shaft drives?

Alan

[Harryg]

I too am confused. Are we talking about sail boats or power boats. Weight is cumulative and an overloaded cat of any size will not perform well under sail. The more weight carried in motors, fuel, water and cruising gear the more friends and family will be left standing on the marina. Harry

[Tropic Cat]

Originally Posted by Harryg

Weight is cumulative and an overloaded cat of any size will not perform well under sail. The more weight carried in motors, fuel, water and cruising gear the more friends and family will be left standing on the marina. Harry

I don't think anyone would disagree. Just as I'm certain you'll agree that an extra 60 kgs will not affect the performance of any cruising catamaran. Yet the extra engine power is available if needed. A win / win situation.

[sailingaway221]

Just put new 2 x Beta 30 hp in my 43 foot cat.....I am very happy with them and the performance and fuel efficiency is amazing. Definitely should add them to the list of possibilities.

[gramos]

All this has me puzzled , I have 2x 10 hp volvos with excellent flexofold 2 blades but still manage 5.6 knots on one engine and 7.5 on two (best) .accompanied by 1.25 litres an hour consumption, all on a 38 ft cat ? whats wrong with my boat ! or are volvos really more hp than stated ?
I would spend more efforts keeping your weight down , this will help your sailing perfomance as well as your fuel consumption . we are , afterall, sailors n,est pas ?

[fastcat435]

Hallo Alan

one can loose up to 75 % on a 2 blade folding racing prop and up to 60 % on a feathering 3 blade prop, the point I am trying to make is that not only the engine HP is important
equally important are the drag and efficiency of power transfer of the saildrive and the prop efficiency,
Some manufacturers of diesel saildrives publish the actual loss from the engine saildrive combination.
The last test that was published was done by Yachting monthly in May of this year
Wonder Down Under. Product tests. Download this article.
Unfortunately the 2 blade racing props where not included in the test but many others where.
The Flex O fold 3 blade performed best while the Kiwi prop was the worst performer for the top speed
The highest speed was 7.65 knots for the 3 blade flex o fold and the lowest speed for the Kiwi was 7 knots.
Another aspect that is very important is keeping the prop clean of any growth, a dirty prop with pox or barnacles can reduce the output dramatically.

[mikereed100]

Originally Posted by Harryg

Weight is the enemy of multihulls. I will installing Lombardinis or Vetus 29hp motors in my 43 foot schionning cat to keep the weight as low as possible. Harry

Harry,

I would do a carefull comparison of cost and availability of parts for the Vetus before committing. I was quoted $600USD for the engine manual alone. An exhast riser, as I recall, was about $2,400. Even sourcing parts through Mitsubishi was very costly. The Kubota-based engines, while a bit heavier, have the advantage that one can buy parts at an automotive (or lawnmower!) shop. One cannot go wrong with Yanmars as they are ubiquitous and parts readily available, but expect to pay almost exactly twice as much for common parts (starters, head gaskets, water pumps etc.,) as the Kubotas.

Best of luck,
Mike

[Harryg]

Mike,

Thanks for the info. I guess that's why Vetus do not feature in many discussions about motors. I wonder if Lombardini have a similar reputation for expensive parts. I may have to go on a diet and include Yanmar in my list of preferred motors.

[Atlantic42]

I have tiny old and heavy Yanmar 2GM20fc engines in my Chris White Atlantic 42 that give me maybe 10hp at cruise speed of 6.5 knots at 2400RPM. Could she use more power? Yes. But, I have time on my side so I do very little motoring and lots of fast sailing. As for the conditions you speak of. I'd hate to be you to dock in such high wind conditions... just think of the weight of fenders!

[Nordic cat]

Originally Posted by fastcat435

Hallo Alan

one can loose up to 75 % on a 2 blade folding racing prop and up to 60 % on a feathering 3 blade prop, the point I am trying to make is that not only the engine HP is important
equally important are the drag and efficiency of power transfer of the saildrive and the prop efficiency,
Some manufacturers of diesel saildrives publish the actual loss from the engine saildrive combination.
The last test that was published was done by Yachting monthly in May of this year
Wonder Down Under. Product tests. Download this article.
Unfortunately the 2 blade racing props where not included in the test but many others where.
The Flex O fold 3 blade performed best while the Kiwi prop was the worst performer for the top speed
The highest speed was 7.65 knots for the 3 blade flex o fold and the lowest speed for the Kiwi was 7 knots.
Another aspect that is very important is keeping the prop clean of any growth, a dirty prop with pox or barnacles can reduce the output dramatically.

Gideon,

You are spouting all kinds of efficiency factors here without any references to actual tests. The test you mention in Yachting Monthly is a comapritive test, and does not say anything about the efficiencies!

What the test does show, is that there is now not much difference between the traditional fixed 3-blade prop and the better feathering and folding units when it comes to thrust and boat speeds.

Do you have hard facts to back up your claim of 25% efficiency on a 2 bladed folding prop used as it should be?

Alan

[fastcat435]

Hallo Alan
You are missing the point , this tread started on engine size alone and the point I am trying to make is that it is not only about engine size but also on efficiency of the drive train ( sail drive or propshaft and gearbox ) and the prop efficiency.
3 tests where made the last 2 years that I am aware of regarding props. Last year in the German magazine segeln, http://www.propelspecialisten.dk/dow..._test_2008.pdf and another test in a English yachting magazine.

Gori three-bladed folding propeller test

What both these test show is a difference in top speed of up to 10 % between the best and the worst performing prop and this is at hull speed or close to it,
A good choice of prop is at least as important as the engine .
I am not promoting any prop just trying to make a point regarding props

[Nordic cat]

The test you linked to is again a comparitive test between different propellers, and does not mention propeller efficiency factors either.

I'm sorry, but I think that you don't really know what you are talking about when claiming 25% efficiency for 2 bladed folding props.

Quote" if you take a 40 hp engine and a 25 % loss of power that leaves you with 30, if you use a 2 blade folding racing prop ( the worst for transmission losses you might end up with only 8 hp to propel your boat." Unquote.

People who know about props generally figure around 65-70 % efficiency for a fast turning fixed 3 blade prop, and higher if its slower.
If you compare this to the compaitive test results in the links above, then your claim is way off the mark.

Engineering and selling are 2 different subjects

Just another exxageration maybe?

Alan