50/50 or 100/100.

I like to have a 100/100 motorsailor not a 50/50 motorsailor.
What is the difference?

 

Hullshape, windage and weight on the sailing side.
Hullshape ,drag of keel, rig and large rudder on motor side.

 

Percentages

50% + 50% = 100% = 1 boat

100%+100% = 200% the answer to this calulation implies you need two boats.

 

Welcome to the club. I want one of those two, but windvang is right, a 100/100 is impossible.

For the old style (traditional) motorsailors I would say : 70 (motor)/30(sail).

For the new concept I would say: 50/50 to 85/75 in all possible combinations.

I am trying to design a 95/50

 

All interpretations are possible but with 95/50 what I want to say is that such a boat only lose 5% in performance to a fast dedicated sailboat and lose about 50% in efficiency to a pure dedicated motorboat.

 

There was a really good suggestion (at least I thought so) somewhere in an earlier thread to list motorsailers by SA/D and HP/D ratios, ie. a 14/14. If I remember I'll add the link to the thread... I think that's a much more informative system, especially when comparing not-quite-so-similar boats.

 

A Motorsailer is a displacement hull and limited to the hull speed.
With existing modern sail system and powerful lightweight engines.
If I can reach hull speed under sail, with the engine/s stopped for me it is a 100% sailing boat.
If I can reach hull speed running the engine/s without sail/s , for me it is a 100% motor boat.

 

Thanks Marshmat. That's my proposed labeling system. SA/D ratio I use is the standard and well known one. For the HP/D ratio I use 6*HP*1000/D, because I've found this matches quite well to compare it with the SA/D ratio (Imperial units)

The benefit of this labeling system, against the "century" rule, is that saying that a boat is a 50/50 motorsailer says nothing about the real sail and engine power of the boat, nor if she's light or heavy, while this new label I propose does. And most of the times this rule derives in the talking about 90/90, 100/100, etc., as it is based in personal perception and opinions, and not in real figures.

Here (again, as it was already posted in the thread marshmat mentions) an explanation of my 'short' labeling system for monohull sailing boats:

Example label: H 14/14

First figure relates to the SA/D ratio (to the closest integer), so to the sailing power, and
Second figure relates to the 6*HP*1000/D coeficient (to the closest integer), so to the motoring power
Letter is related to the D/L ratio, as follows (monohulls):

VL = Very low D/L ratio, under 100
L= Low D/L, from 100 to 200, typically 150
M = Medium D/L, from 200 to 300, typically 250
H = High D/L, from 300 to 400, tipically 350
VH = Very Heavy D/L, over 400

So, a sailing boat (monohull) with a D/L ratio of 356, an SA/D ratio of 14.45 and an HP/D ratio of 2.3, would have a label like: H -14/14

- If ratio in label is greater than one, the boat is sailing oriented. If less than one, motoring oriented.

Applying it to a motorsailers definition:

- If first figure is 14+ the boat has plenty of power under sails alone. Lower than 10 seems too low sails power to me for a motorsailer: The boat should rather be considered a "sail assisted motor boat". Definitively if under 8. If higher than 16 the boat should probably be better classificated as a sailing boat having more or less engine power.

- Second figure (motor) being over 18 means quite an excess of engine power, in my opinion. A figure under 9 will indicate the boat is a sailing boat with auxiliary engine, rather than a motorsailer. For an efficient motorsailer, it should be around 14, let's say from 12 to 16.

- What are called 50/50 motorsailers by the "century" rule (Or 90/90 or whatever you want), become 14/14 (more or less) under this labeling system.


That's the basic thing. We can also add some letters at the end of it, to better explain the intended design (Or marketing!) concept, as MS for Motorsailers, PH for Pilot House, RS for raised saloon, OC for ocean cruiser, CC for coastal cruiser, etc, etc.

So, if we read something like M 16/12 RSOC, we can understand the boat is a "medium weight, sail oriented, raised saloon ocean cruiser" most probably with a good performance under sail and with an engine allowing for economic motoring passages but having yet enough power reserve to beat to winward in a gale in protected waters.

Going further, we can try to look for how to better enphasize and define some subtle but most important differences like the ones between boats labeled as M 14/14 CCPH and M 14/14 OCPH. To this end, and using what's already available in the industry, we can add the UE Category Design letter (A, B, C, D) which in a very precise way defines the designed weather-coping ability. So we arrive to the very precise (maybe to precise to be easily remembered):

'Labeling System'
Example: M A16/12 PHMS

We labeled here a real ocean going, medium weighted, sails-only oriented, nicely powered, pilothouse motorsailer. A whole lot of a definition. And a whole lot of a boat.

For those not familiarized with the UE Design Category, here you have the meanings:

- A, applies to boats designed to cope with winds in excess of force 8 and waves over 4 m (significative height). Oceanic.
- B, to boats designed to cope with winds up to force 8 and waves up to 4 m. Short open seas passages.
- C, to boats designed to cope with winds up to force 6 and 2 m waves. Coastal sailing.
- D, to boats designed to navigate in protected waters, maximum force 4 and 0,5 m waves.

If some of you are interested in knowing more, plase visit the pages:
http://www.xente.mundo-r.com/motorsailers/index.htm

 

On a good sailboat with a proper engine & sailing prop installed , the ONLY thing you loose is for the WEIGHT of all the installed machinery and equippment & fuel carried.

Deduct 10% from 100% sail for the weight.

On a motorboat the only disadvantage is the extra windage lost due to the rigging , and the internal space lost for sails.

Deduct 10% from a good displacement motorboat.

Result a 90/90 can easily be envisioned .

FAST FRED

 

Why don’t add 10% on the sail area and 10% on the engine power and you have the 100/100.

 

If you remove the engine you can have more ballast and then you can add more sail.
If you install a bigger engine you have to remove more ballast and then you have to remove more sail.

 

If you remove the engine it will not be a motorsailer.
A more powerfully engine doesn’t mean more weight.

 

OK, you can have a modern lightweight engine, but if you want a 120HP diesel that's probably 400kg(?) while a 30HP is more like 100kg(?).
Most diesels burn 0.2kg or so per hour per hp, so you need more fuel for the bigger engine.

I think you can get a good 90/90 with light displacement, lightweight engine and maybe a lifting keel.

 

I agree on the first 90%, for sail ability, but for having the same capability of a motorboat I would say that you had to have the power to make 3/4 of hull speed in a moderate gale (40 knots of wind on the head, and 4 to 5 M waves). I don't know for sure, but I suppose that in a 10 ton, 42 foot motor boat, for doing that you will need something like 150hp.

If you put that engine weight in a sailboat you can say goodbye to the 90% sail ability.

I would rather maintain the 90% of sail ability with a 50% motor ability, that would be ( in the same moderate gale situation), the ability to make a little bit more than half of the hull speed, and for that I guess that something like 75hp is enough.

That’s why I think that a 90/90 is, or impossible, or very difficult to get (maybe not so difficult in big sail boats).

 

I think your engine should allow you to deal (motoring alone) with gale force head winds in sheltered waters, not open seas with 4-5 m waves. Maybe that's too much and, with a fixed propeller you'd have to slow down rpm just not to overload the engine if you have to motor for a long time. So probably 150 HP for a 42' 10 ton boat is much more than needed.

As an example, Victorie 12.70 (http://www.victoire.nl/schepen.php?boot=7) mounts a 55 HP engine, which gives her an 6*HP/D ratio of 16.62 which is, in my opinion, good enough. And that boat has an SA/D ratio of 15.27, so probably a nice performer under sail too.

When in a gale in open waters, if you have to motor, you'd probably will not try to go directly into the wind, but motorsail into it at an open angle with the proper set of sails. That's wiser and that's what motorsailers are good for.

Cheers.