Motor Sailers?

[Guillermo]

Here you have my definition for monohull motorsailers:

"Motorsailers should be, in my opinion, hybrids among sailing boats and motor boats, with amplier volumes than those of a pure sailing boat (And to my taste with a nice pilothouse!) to make them more livable and able to carry a generous cargo; have manegeable sails but able to easily develope hull speed under sail alone; have a propeller-engine combination allowing for a fuel efficient motoring and with power enough to reach hull speed, as well as some extra muscle to beat dead to winward in a storm (force 10) in protected waters.
This means, to me, an SA/D ratio from 13 to 15 and a HP/(D/1000) ratio from 2 to 2.5 (Imperial units)
D/Lwl ratio may go from 250 for lighter ones as in many modern designs bred in sailing boats, up to 450 for heavy-weigths long keelers bred in fishing boats"

[Mikey]

Many sailing boats of today are overpowered, but I would still say that a HP/(D/1000) ratio of 2 - 2.5 is a bit too low for a proper motor sailor.

That would give a 45,000 lb 50 footer a 90 to 112.5 hp engine. 90 HP is more than enough for normal motoring but not quite enough to safely get out from a dangerous shore in force 10 winds.

I would go for a bit more, 2.5 - 3 => 112.5 to 135 HP, enough also for not protected waters. Opinions?

Mikey

[mackid068]

Hm, maybe 4 hp/ton or is that reaching?

[marshmat]

I wouldn't think so... with old finicky diesels that might be too much for normal cruising, but modern engines work just fine at low speed (and more efficiently than a smaller engine at high speed). If your engine's flexible enough to handle the wide power range you need, I'd much rather have the extra power for when I need it....

[mackid068]

so 3hp/ton is good?

[asathor]

How about 3.478915

You really should go sailing instead of worrying about such numbers.

Just keep in mind that you need 3.14 times the power required to obtain hull speed when going to winward in a blow - Leonardo Da Vinchi actually noticed this during a heated conversation with the pope.

[FAST FRED]

The problem of only having enough power to motor efficently in a calm ,
VS the huge ( 3x+)amount of power needed to buck a high wind is NOT an easy one to solve.

The usual setup where the engine is set to run full power at full RPM stinks royally at efficency when used at low cruising speeds , or worse when the vessel is getting a sail assist.

The engine will usually respond to this severe underloading with "wet stacking" , where unburned fuel (too light load) blows by the rings which do not have enough operating pressure from combustion to seal properly.
The cylinders will be burnished and loose their oil retaining ability , so wear out even faster. The lube oil will be contaminated with blow by , the acids produced raise heck with the bearings. UGH!

Traditional M/S would use a variable pitch prop , oversized diameter (cruising setup) that with normal pitch would never be able to pull the mfg recomended full throttle RPM.

However at low engine speeds the extra prop diameter was great at absorbing a higher amount of engine power , so the engine would last longer.

In a gale the engine would be run at higher RPM with much of the pitch taken out , which allowed the RPM and more closly matched the slower speed made good by the vessel.

The better solution would be a multi speed transmission , which is fairly easy to engineer.

Most LARGE truck trannys are built for cont. operation in any gear and at the low power required for a moderate sized vessel 35 to 70 ft , would only be operating at a fraction of the power a modern truck (350 to 500HP) produces.

The variable pitch props come with thrust bearings built in (Hundstatt) so hookup would be quite easy, and the engine could be very soft mounted for maximum quiet and vibration controll.

10th, .82, 9th, 1.00, 8th, 1.26, 7th, 1.59, 6th, 2.00,/// 5th, 2.57, 4th, 3.14, 3th, 3.95, 2nd, 4.98 and 1st, 6.27. Low R, around 6.27, High R, around 2.00 to one

Depending on how light the M/S is and how much sail assist , the ratios from 7th to 3rd would look promising for light and heavy weather, as well as light and heavy fuel tanks.

The only "extra" expense would be for a REQUIRED exhaust temp gage (EGT) a hunderd bucks or so to keep the engine operating with out any overload.

Bigger diesel truck engines are easy to marinize , simply requires either a wet exhaust manifold , or loads of insulation for the engine room lead to a prefered dry stack.

With a modern 3 stage injection the computer could maximize the economy , and overload would be impossable .
But there would be no way to "get Home" after a lightning strike , so the older noiser less efficent mechanical injection might be a better offshore cruiser.

FAST FRED

[Vega]

FastFred said:
"Traditional M/S would use a variable pitch prop , oversized diameter (cruising setup) that with normal pitch would never be able to pull the mfg recomended full throttle RPM".





If you can change the prop. pitch I don't see the problem. Looks to me that the effect would be close to the one produced by a a multi speed transmission.

[Guillermo]

Originally Posted by FAST FRED

....But there would be no way to "get Home" after a lightning strike , so the older noiser less efficent mechanical injection might be a better offshore cruiser.

FAST FRED

Keeping things simple, reliable and easy to maintain seems to me a basic requirement in pleasure boating when cruising around.
(I'm talking about the average short handed cruiser, not the chartering or the luxury segments)
I do not have experience with modern trucks diesel engines and their sofisticated reduction system, but maybe it will add an extra complication to something that should be as simple and reliable as possible in a boat: the mechanical propulsion system.
So, for an all around proper motorsailer, I vote for a medium revs diesel engine, rated as to its power come into in the 2 to 2.5 HP/D factor range I mentioned before, mechanical injection, hydraulic reduction gear and an effective 3 blades fixed propeller or Autoprop type.
Answering Mikey, in Thailand: To clew off a lee shore with formed seas we'd rather be motorsailing, not only motoring (except when a rig failure, of course). So I think we do not not need more engine power for that. I find that going up to 3 in the ratio, or even more, is more related with semi-displacement hulls with flatter stern sections, designed rather for short waters hopping in mind.
Guillermo.

[mackid068]

Does anyone here think that an aft pilothouse is nice?

[FAST FRED]

Nice or not its the prefered place if the boat will cruise and stay on her own anchor gear for long periods.

The foward houses make for very "nervous" boats at anchor , that frequently need multiple anchors to keep steady in most winds.

Most Fish boats tie up to the dock , in port , an advantage not usually open to the wandering cruiser.

The feathers are on the BACK of the arrow (or weathervane) for a reason.

FAST FRED

[Vega]

mackid068 :

"Does anyone here think that an aft pilothouse is nice?"


I like this one:


http://www.morrisyachts.com/photos_my51.html

[brian eiland]

Originally Posted by Vega

mackid068 ....an aft pilothouse is nice?"
I like this one:
http://www.morrisyachts.com/photos_my51.html

I'll agree with you there. Or how about this one:
http://boatdesign.net/forums/attachm...achmentid=2049

....image located under another thread, "Perfect Cruising Boat"

[Vega]

Yes, there are new boats...I would say the new breed of motorsailors that are not fat anymore, even the small ones. Look at this 39ft. Not close to the Morris in beauty, but not ugly...and that one I can afford it (probably).

http://www.siltala.fi/385prelim/3853-d.jpg

[mackid068]

I, myself, especially for motor trawlers, am a big fan of aftpilothouses.