How to turn a Traditional Motorsailer into a Sailing Boat

[Laminar Flow]

This is how we did it with performance examples in the second half. Enjoy!

 

[B27]

Is the main difference between a 'sailing boat' and a 'motorboat with a mast' , the nut on the end of the tiller?

 

[srm]

Must confess to having liked the idea of a proper wheelhouse for northern waters but was put off by the usual lack of sailing performance. Very interesting to see the mods and how well your boat performs. Also, a well produced video that keeps to the point.

 

[Laminar Flow]

Is the main difference between a 'sailing boat' and a 'motorboat with a mast' , the nut on the end of the tiller?

I would say that it is the SA/D ratio.
A Motorsailer, according to Brewer, should have a SA/D ratio of between 13 and 14.
Ours, calculated over volume of displacement for saltwater is 17,98, or mid range cruiser/racer (17-19).
That is reflected in her performance.

Best, A.

 

[B27]

I would say that it is the SA/D ratio.
A Motorsailer, according to Brewer, should have a SA/D ratio of between 13 and 14.
Ours, calculated over volume of displacement for saltwater is 17,98, or mid range cruiser/racer (17-19).
That is reflected in her performance.

Best, A.

Sail area is one thing, ability to windward is another.
A cruising sailing boat seems to spend significant time sailing to windward , reefed, so bar-room SA/D ratios are out of the window.
Don't misunderstand me, I think it's great if you put up more sail and turn off the motor.
I see lots of boats which could be sailing, motoring from A to B.
If you want to rely on sails, the two biggest issues are 1) light winds and 2) going upwind.

That's taking for granted we're happy to use motors at close quarters entering port etc, I'm comfortable with that.

Also not everyone cares about 'normalising' everything with a ratio.
If you've got a 33ft boat which gets from here to Weymouth in the same time as my 27ft boat, why would I be scoring points about ratios? If we've both sailed there before the pubs shut using, minimal diesel, we're pretty equal?

 

[oldmanofthehills]

As I have commented elsewhere I have increased the Sail Area of our LM27 by 13% by means of a short 1m bowsprit and 20% increased genoa area.

On the right tack in the right airs she does have about a 7% increase in speed compared with her old sail in the same condition. Very pleasurable and I am glad I did it.
However it was partly done to move the centre of effort forward as the LM27 suffers from inconvenient weather helm which is hard to manage as the spade rudder is too small. (She still has slight helm even with fully reefed main). I have increased rudder area upwards but the profile of the hollow GRP rudder was nearly ok as it was, so did not change it - however it did not greatly improve handling.

But and its a big but, as a shallow draft long keeler she is slightly more tender and furling and reefing is critical much more than our old heavy Westerly ketch, and I have made it possibly more so. I practice we just reef the main early and tweak the genoa, though its then hard to get ideal genoa shape

Further more I have not improved windward performance as if I press beyond about 50 degrees she simply goes leeward more rather than the apparent heading.

So perhaps I need to improve the profile of the deadwood though it seems not a poor as the Colvic W looking at the pictures

 

[oldmanofthehills]

And thanks for the Video, Laminar F

 

[Supertramp]

A well put together informative video. You have ended up with the perfect rig.

My Cromarty 36 is similar - a few feet longer (34.5ft × 12ft hull) and with gentler, more yacht like sections around the stern, and slightly shorter LWL. The deadwood has some tapering and the rudder is partially balanced and with an aerofoil section. The freeboard is a lot less than yours and the decks are not always dry!

I carry a little less sail than you and I rarely push the speed beyond 6.5 knts. Downwind tracking is a revelation. My windward performance is similar to yours - boat speed is necessary to keep the leeway down, and "pinching" close to the wind is pointless. On any point up to a reach she can be balanced to sail with the helm lashed more or less central and has crossed the Irish Sea like this. Otherwise I use the autopilot.

I have no accurate performance data. I am easily outpointed and overtaken by cruiser racers but show similar performance to cruising yachts, especially those with full cruising gear, furling mains etc. At least in winds above 10 knts. But absolute speed doesn't worry me - I value the ability to keep up good passage times whether the wind is favourable, too strong or too light (using engine).

However I have not yet mastered close quarters maneuvering. Going astern is a lottery. Dealt with in other threads.

The point is that you end up with a boat that has an interesting compromise between performance, accommodation and comfort.

 

[William_H]

Just picking up on oldmanofthehills' comment re weather helm and centre of effort of sails. This concept of cof e of sails versus centre of lateral resistance of hull/keel does work nicely in conditions of gentle breeze and flat boat.
I think however that as soon as you heel the boat with a bit of strong breeze the non symetrical shape of the hull in the water and sail drive being to lee ward, causes weather helm effect that is much more powerful than any effect from sail pressure balance. Now the power of this weather helm from heeling does vary with boat shape but in the case of my little boat is very severe. Needs a large rudder to control. But mostly sail area reduction either jib or main. ol'will

 

[Supertramp]

Just picking up on oldmanofthehills' comment re weather helm and centre of effort of sails. This concept of cof e of sails versus centre of lateral resistance of hull/keel does work nicely in conditions of gentle breeze and flat boat.
I think however that as soon as you heel the boat with a bit of strong breeze the non symetrical shape of the hull in the water and sail drive being to lee ward, causes weather helm effect that is much more powerful than any effect from sail pressure balance. Now the power of this weather helm from heeling does vary with boat shape but in the case of my little boat is very severe. Needs a large rudder to control. But mostly sail area reduction either jib or main. ol'will

I agree with this - getting the sail plan balanced for a given point of sailing and wind strength makes a big difference. You can hang on to full sail in strong winds but everything is much easier and barely slower with some main rolled in or mizzen dropped. Perhaps its part of the reason why a ketch rig is popular on these sort of boats.

 

[Laminar Flow]

In regards to weatherhelm:
The Watson is not a balanced design. I have done the calculations for ours and a 25.5 and neither has enough lead. Worse yet, the flat, sharp-edged rudder stalls out as soon as it gets any modest loading. Furthermore the rudder is some 40% too small for a long keel sailing vessel. It's a lose/lose situation.

On the other hand, the hull has great beam and, together with a hefty displacement, this provides tremendous sail-carrying power for a 31.5 footer. Without doing the calculations, I would never suggest that anyone substantially increase their sail area. We were able to more than double the SA of the original model (214% increase), while retaining a wind pressure coefficient suitable for offshore ocean work.

Windward ability is governed by two factors: the hull and the rig.
For what its worth and with it's shorter luff lengths and increased drag, a ketch rig is about 20% less efficient to weather than a single-masted rig, assuming a sloop were 100%. (cutter 95%, schooner 70%, ketch 80%).
At 15% of SA our Watson's lateral plane is still in the ballpark for a long keel boat, even with our much larger SA. The myth that long keels don't go to weather is just that, a myth. Not so long ago all boats looked just like ours below the water and, without the benefit of an engine, the lack of reliable windward performance would have been a death sentence. Finally, lift increases with to the square of the speed. Speed is your friend when going to weather. This is only limited by a vessel's stability. Fortunately, we have lots of that.
In conclusion, her windward ability is absolutely adequate for a cruiser. That said, we do not like sailing more to weather than we have to and certainly not over long distances. Given the choice we'd rather stay in port and sample the offerings of a few more distilleries, visit the local attractions or go for a walk up a mountain. As we seem to get around quite a bit in our ship, there is a good chance that we actually know what we are talking about. This year we made it up to the North of the Shetlands and back to our port in Brittany, all the while with several of the passages being close hauled and on occasion in rather lively weather.

Best, A.

 

[Laminar Flow]

I forgot:
Much fuss, perhaps too much, is made of windward ability and at the cost of everything else, though the current crop of planing types seem to do much better downwind than their immediate forebears, albeit also at a sacrifice in windward excellence.
I have many, many tens of thousands of miles of offshore sailing experience, but I am continuously blown away by this (modified) boat's ability to track downwind at, for her type, quite impossible speeds and to do so, steep quartering sea or not, under the guidance of a slow-witted autopilot.
Horses for courses ...
A.

 

[flaming]

I forgot:
Much fuss, perhaps too much, is made of windward ability and at the cost of everything else, though the current crop of planing types seem to do much better downwind than their immediate forebears, albeit also at a sacrifice in windward excellence.

Really interesting video, and you've done a great job in making a boat that suits you. I'm actually amazed that original rudder got signed off for production really!

Just to nit pick on one point - the most recent planing types are not really giving up windward performance. As discussed in several threads now, boats like the JPKs, Sunfasts, Class 40s etc, that are capable of getting up and boogying downwind were demonstrably faster to windward over the heavy airs beat to the fastnet rock last summer than their non planing predecessors.
And in more normal AWB land, the Sunsail skippers I know reported that, much to their surprise, their new "fat boy" Jeaneau 410s are demonstrably faster upwind than the First 40s that they replaced. In all except very light winds. They had a season of racing them together and apparently it was very quickly clear that the older boats were noticeably slower.

 

[fredrussell]

I suppose for many motorsailer owners, the limiting factor will be the cost of new spars and sails etc to follow OP’s lead. I would assume the cost of larger spars and rigging alone would be more than the value of the boat itself, and then a whole suite of sails is required. That said, as someone who sails a ‘non-deckhoused’ year round in the UK, I watched the vid with great envy!

 

[Laminar Flow]

I suppose for many motorsailer owners, the limiting factor will be the cost of new spars and sails etc to follow OP’s lead. I would assume the cost of larger spars and rigging alone would be more than the value of the boat itself, and then a whole suite of sails is required. That said, as someone who sails a ‘non-deckhoused’ year round in the UK, I watched the vid with great envy!

There are plenty of older boats going to the tip these days and I can't imagine it being overly difficult finding a longer spar at a reasonable cost.
Additionally, not every type is suitable for that kind of dramatic SA increase. Quite a few models have rather slack bilges and limited initial stability. I saw pictures of a Fisher 34 in NL that had been "pimped" with a much taller mast and which, consequently, seemed to be sailing at rather startling angles of heel.
The Watson hull has much firmer bilges and less capsizing volume deep down, a higher centre of buoyancy and a lower beam/length ratio (beamier hull). Hence: do the math first.

Just to nit pick on one point - the most recent planing types are not really giving up windward performance. As discussed in several threads now, boats like the JPKs, Sunfasts, Class 40s etc, that are capable of getting up and boogying downwind were demonstrably faster to windward over the heavy airs beat to the fastnet rock last summer than their non planing predecessors.
And in more normal AWB land, the Sunsail skippers I know reported that, much to their surprise, their new "fat boy" Jeaneau 410s are demonstrably faster upwind than the First 40s that they replaced. In all except very light winds. They had a season of racing them together and apparently it was very quickly clear that the older boats were noticeably

My comment was based on the assessment and analysis by Eric Sponberg, who, himself, designed a few of these types (retired now, I think). If things have improved then, that is probably a good thing.

The moment something like that becomes available with a heated wheelhouse, as well as the carrying capacity for near enough a 3/4 ton of fluids, provisions for 2-4 months of expedition cruising, all the mod coms of home, three anchors with gear and all rest of the usual and necessary cruising tackle, tools and bicycles, and, moreover, all in a close to 30' package, I promise to pay more attention.

Best, A.

 

[flaming]

My comment was based on the assessment and analysis by Eric Sponberg, who, himself, designed a few of these types (retired now, I think). If things have improved then, that is probably a good thing.

The moment something like that becomes available with a heated wheelhouse, as well as the carrying capacity for near enough a 3/4 ton of fluids, provisions for 2-4 months of expedition cruising, all the mod coms of home, three anchors with gear and all rest of the usual and necessary cruising tackle, tools and bicycles, and, moreover, all in a close to 30' package, I promise to pay more attention.

Best, A.

Well, we've debated that point over lots of threads... So you have seen the race results before now...

And yep, as discussed before, where in the past wide boats were generally fat in the backside but still comparatively pointy up front, the latest designs are pushing that volume forward, and getting clever with chines etc to give them much better windward performance than before.
There are boats marketed at the expedition market that are of that wide type, but nothing that small, and nothing that you wouldn't need a decent lottery win to afford....

You've clearly done a great job making your boat into a sailing boat. I think the rudder mods are particularly impressive.

 

[Supertramp]

Additionally, not every type is suitable for that kind of dramatic SA increase. Quite a few models have rather slack bilges and limited initial stability. I saw pictures of a Fisher 34 in NL that had been "pimped" with a much taller mast and which, consequently, seemed to be sailing at rather startling angles of heel.

A good point, and if a motorsailer was designed to sail well to begin with you shouldn't need to make radical changes. I think the Fisher 34 suffers (and benefits) from a very heavy displacement for its length, and its not especially beamy. Something like 4.8 tonnes of ballast, and 11.5 tonnes displacement! A lot of 37's have a bowsprit similar to yours presumably to up the sail area, and bring the centre of effort forward.

The Cromarty was designed by the same team who designed Fishers, but over 10 years later. I like to think they transferred a lot of good ideas from their earlier designs while choosing a very different hull shape and a lighter overall weight (8.5 t vs 11.5 t for the 34). 8.5 t is heavy enough and I get upset if we heel more than 15 degrees. But nothing punches through seas like heavy displacement which is when I wish for the Fisher, or Colvic.

I fully agree about the challenge of finding up to date pilothouse cruising yachts that can operate independently for several months without cans strapped all over the deck. Not easy to achieve under 35 feet.

Sirius 35 and Bestevaer 36 offer something near but well beyond my means. Interesting to see a modern motorsailer based on a modern wide bowed design. Peter Goss's Oddity is interesting and embodies a lot of good features but as with many modern designs loses out on the sheer displacement benefits.

 

[38mess]

Love a warm dry wheelhouse, I couldn't imagine sitting in the rain wind and cold sailing a boat now, also gets you out of any sun we get in summer time.
It looks a great job, I have seen CWs in yards and always noticed the rubbish rudder and thought it looked like an afterthought.

 

[thinwater]

I noticed the use of both "," and "." as decimal separators (SA/D given as 17,98, but later the boat was described as a 31.5-footer). I've worked with Spaniards that use "." for thousands and "," for the decimal separator.

ISO and IUPAC use either comma or period, and the spaces for thousands on both sides of the decimal. 1 000 000,000 01 vs. 1,000,000.00001 US practice.

Interesting, and potentially confusing, as an engineer working in several areas. You are never sure if you are looking at a typo. Decimal separator - Wikipedia

 

[DownWest]

Really enjoyed that video. Clear goals and thought out solutions that resulted in exactly what you aimed for.

Sort of beggers belief that the deadwood/rudder was not addressed by the builders earlier.