Baby Bluewater Cruiser

[Stemar]

I came across this today

Not for me - my idea of blue water sailing is Weymouth from the Solent, and I'd drive myself mad crossing oceans alone, but an interesting concept.

Do bilge keelers really roll less than fins?

 

[Black Sheep]

Very interesting.
There's now a video of a discussion with the naval architect:

Discussion of the bilge keels starts at 18:05

 

[Blueboatman]

Do bilge keel roll less?
Yes
Can you change the roll moment by easing a junk sail up or down the mast a few cm?
Yes
Did I have a blue junk rigged bilge keeper once ? Ah, yes ?
Bluewater ‘n all , happy memories , lots of ‘em

 

[matt1]

In my experience, yes, twin keeled boats roll less downwind and surf a bit earlier than their fin keeled sisters (to be clear, I'm talking modern variant twin keels here)

 

[Tranona]

Maurice Griffiths always made the point that the bilge plates he added to his long keel boats did dampen rolling - but remember the boats he was taking about were fat round bilge with shallow draught. I removed them from my Eventide when I increased the draft and don't think it rolled any more afterwards, but of course that was a chine boat and the deeper keel probably had an effect.

 

[Wansworth]

Going o be a very interesting series of vids,experienced small boat ocean sailer commissioning this boat

 

[Laminar Flow]

Maurice Griffiths always made the point that the bilge plates he added to his long keel boats did dampen rolling - but remember the boats he was taking about were fat round bilge with shallow draught. I removed them from my Eventide when I increased the draft and don't think it rolled any more afterwards, but of course that was a chine boat and the deeper keel probably had an effect.

Mr. Griffiths actually said that the chine had more of an effect on roll attenuation than the fins, this when commenting on the Golden Hind design. Ex-owner of a Water Witch myself.
Roll attenuation is also more effective at speed and particularly so with low aspect fins as they are much more stall resistant. Much of what is generally attributed to the supposed roll reduction of bilge or twins is due to to a reduction in the radius of gyration by having shallower draft, much as the effect of raising the height of the relatively heavy junk sail and therefore making the boat a little "less" stable or changing the roll period versus roll inducing wave period.

I do not see much improvement over Benford's dory offerings which are also available with twin keels and look rather similar. Of course, in North America bilge/twins are exotic. To be honest, I was not overly impressed by the architect and I do not see how drawing parallels to anti roll keels on naval ships is overly helpful when designing keels for a sailing boat. Not much new there.

 

[Laminar Flow]

I just looked through the numbers and I would think that the projected displacement numbers are highly aspirational.

Supplies (food and water) for "at least 60 days" come in at about 900lbs add to this the weight of the crew, about 160lbs, that is a grand total of 1060 pounds and that does not include any other gear or personal effects.

I'm not sure he will find this boat much, and certainly not considerably, faster than the Contessa.
The "real" SA/D ratio of the Contessa is about 16, assuming a displacement of 5400lbs.
The new build with a projected full load displacement of under 3000lbs (highly unlikely) has a SA/D of 17 which is marginally more. And when the true displacement figures show up this will be even lower. There will be a modest advantage going down hill with a single junk rig sail over a Bermudan sloop, unless the latter decides to fly a chute.
In a contemporary context, a SA/D ratio of 17 is modest. The designer Phil Bolger, who was not afraid to walk off the well-trodden path, suggested that one should make a Chineese lug as large as possible since it is easily reefed and adding light weather additions is not necessarily practical or possible.

 

[Blueboatman]

Iirc my lugsail was 25% greater in sail area than the many hundreds supplied with a usual main/genoa.

Consequently it was prudent to ‘reef’ downwind by a factor of +one panel, earlier.

I would suggest that the wretched rolling motion going down the trades ( or across them?) has much less detrimental effect on a battened flat sail. Going upwind is a different matter without any sort of slot between main /foresail nor camber on the sail
The partial balance of the single sail spread either side of the mast helps enormously to keep the helm light and the boat on track without inputting rudder correction, particularly on the roll . Headsails get pretty weird when rolling without a Twizzle set up .
This equates to more, quieter and judderfree, easier miles notched up per 24 hours. Which is nice . And useful

I might then go on to suggest that given the above , the overloading of a small hull in cruising mode is probably less detrimental to sailing performance off wind because roll/back roll doesn’t stall out the sail in quite the same way as a with a high aspect triangle abaft the mast , or a pair of headsails floating aloft.. but this is a tentative thought

Then finally the fishingrod like bend of an unstayed mast acts as a really useful damper to counter roll each moment, every time! Again, less yaw, less rudder input, less braking , more miles sailed, sail area for sail area aloft..
All in all , I found that doing-or using- exceeded what I saw on paper
I am writing relative actualperformance , not exact numbers on a formula fixed in space and time.
I am sure things have moved on
I am as wary as anyone of zealots in the design arena making absolute or bold claims. We shall see

An interesting project for someone , perhaps

 

[Laminar Flow]

Sir Henry Piggot's average speed for a boat of similar length and rig was 3.5kts, granted, "real life" heavier and smaller SA.
Average, real life speed for displacement sailing craft is, in relative speed terms, 0.9 (times sq root DWL). This works out a 4kts for the 21' DWL of the projected design. In this respect, Sir Henry's averages during his circumnavigation, btw, were spot on.

My neighbour built a stitch & glue to a design by Sam Devlin and of similar dimensions. He did a very fine job of it and was awarded fist prize for it at the Port Townsend wooden boat show for "Best New Build". The amounts of ply (9mm) and epoxy that goes into even a modest boat are staggering and it is much more difficult to keep weight down in a small design, particularly if she is to cross oceans.
With a projected D/L ratio of 100, the proposed design approaches that of a Pogo 650 and I doubt that is achievable with what is essentially a low tech approach, amateur construction and a rig that is likely to weigh more than twice that of the Pogo's carbon spars at near half the working SA . There is a reason why super light weight craft are also super expensive.

 

[Wansworth]

Sort of related would be design that the spars fitted in the loa. of the hull and the rudder was within the overall length so could be stored and or transported with no bits overhanging

 

[Tranona]

Mr. Griffiths actually said that the chine had more of an effect on roll attenuation than the fins, this when commenting on the Golden Hind design. Ex-owner of a Water Witch myself.
Roll attenuation is also more effective at speed and particularly so with low aspect fins as they are much more stall resistant. Much of what is generally attributed to the supposed roll reduction of bilge or twins is due to to a reduction in the radius of gyration by having shallower draft, much as the effect of raising the height of the relatively heavy junk sail and therefore making the boat a little "less" stable or changing the roll period versus roll inducing wave period.

I do not see much improvement over Benford's dory offerings which are also available with twin keels and look rather similar. Of course, in North America bilge/twins are exotic. To be honest, I was not overly impressed by the architect and I do not see how drawing parallels to anti roll keels on naval ships is overly helpful when designing keels for a sailing boat. Not much new there.

The original MG reference predates chine designs and was related to the development of the Lone Gull hull form. Lone Gull I was a centreboarder with a relatively flat bottom shallow keel and wide beam. Among other things she rolled a lot downwind and at anchor. The other negative feature was the coachroof which turned out very flexible, particularly because of the forces from the mast leading to leaks around the carlins. So when revising the design to what was originally his personal boat and later a sort of semi production boat, the 3 main changes were deeper keel, no centreboard, narrower beam (9' against 10'), bilge plates (in an effort to dampen rolling) and full width coachroof. One of our club members has what is probably one of the last wooden ones built, albeit with a conventional coachroof and has no complaints about rolling. (See 60 Years a Yacht Designer pps 82-86 for a full discussion on the design development)

My view is that is that it is subjective and ideas of what constitutes excess rolling is very personal. Difficult to assess objectively partly because there are very few, if any boats that are built with or without chines or even with or without bilge plates so difficult to make like for like comparisons. Even the comparative tests on boats that have fin or twin keels as options really only compare pointing ability and speeds on typical windward/leeward courses. My own experience with my Eventide of deepening the keel by about 1', filling in the gap between the keel and the skeg so it looks like the full keel version or a Riptide and building a new higher aspect ratio rudder (still inboard) was overall a major improvement. However, I also moved the forestay forward 6 inches and fitted new sails, restoring the original mainsail area by increasing the foot and having greater roach, so it is difficult to identify which of the changes did what!

Would guess that MG would have felt much the same as he said Lone Gull II was a far better boat than the original and he kept it for many years. His last boat Kylix had essentially the same hull form, although he reverted to a centreboard as she was kept on a shallow Deben mooring whereas Lone Gull II sailed the English Channel.

In agreement with your observations on this new design. Draws very much on Benford's dory designs, but whether it can be built and equipped to the design displacement is doubtful, as is achieving the sort of passage times envisaged. Hope it gets built, though.

 

[Laminar Flow]

The original MG reference predates chine designs and was related to the development of the Lone Gull hull form. Lone Gull I was a centreboarder with a relatively flat bottom shallow keel and wide beam. Among other things she rolled a lot downwind and at anchor. The other negative feature was the coachroof which turned out very flexible, particularly because of the forces from the mast leading to leaks around the carlins. So when revising the design to what was originally his personal boat and later a sort of semi production boat, the 3 main changes were deeper keel, no centreboard, narrower beam (9' against 10'), bilge plates (in an effort to dampen rolling) and full width coachroof. One of our club members has what is probably one of the last wooden ones built, albeit with a conventional coachroof and has no complaints about rolling. (See 60 Years a Yacht Designer pps 82-86 for a full discussion on the design development)

My view is that is that it is subjective and ideas of what constitutes excess rolling is very personal. Difficult to assess objectively partly because there are very few, if any boats that are built with or without chines or even with or without bilge plates so difficult to make like for like comparisons. Even the comparative tests on boats that have fin or twin keels as options really only compare pointing ability and speeds on typical windward/leeward courses. My own experience with my Eventide of deepening the keel by about 1', filling in the gap between the keel and the skeg so it looks like the full keel version or a Riptide and building a new higher aspect ratio rudder (still inboard) was overall a major improvement. However, I also moved the forestay forward 6 inches and fitted new sails, restoring the original mainsail area by increasing the foot and having greater roach, so it is difficult to identify which of the changes did what!

Would guess that MG would have felt much the same as he said Lone Gull II was a far better boat than the original and he kept it for many years. His last boat Kylix had essentially the same hull form, although he reverted to a centreboard as she was kept on a shallow Deben mooring whereas Lone Gull II sailed the English Channel.

In agreement with your observations on this new design. Draws very much on Benford's dory designs, but whether it can be built and equipped to the design displacement is doubtful, as is achieving the sort of passage times envisaged. Hope it gets built, though.

In retrospect, my Water Witch had terrible weatherhelm and she wasn't particularly quick either, but she was my first own boat and you rarely forget your first love.

There are some boats that were built as multichine or round bilge options, but I never have seen a comparative evaluation on them in terms of roll attenuation. Bruce Roberts made a career out of it ...

There were boats built with and without bilge keels, though, and on the same hull.
A point in case were the Colvic Watsons. Though not designed for bilge plates in the first place, many owners added them for drying out purposes. Performance wise they do not do the boats any favour and in some cases have been detrimental to not just sailing performance, but also sail balance. There have been observations made that it made the roll behaviour worse. I would attribute that to adding ballast to an already stiff hull. In this instance any roll dampening effect the keels might have had was negated by the increase in RM. This is supported by remarks that when exchanging an old, heavier engine for a newer much lighter one, in effect reducing the "ballast ratio", the tendency to roll was much reduced. The main ingredient in reducing rolling with additional keels is speed. The Watsons, never too quick in the first place and crippled by poor design in key areas, do not need further help in slowing down, such as by adding extra wetted area and keels of indifferent hydrodynamic quality.

In a similar vein, when the Banjer motorsailers, that have a very round bilge, increased their SA from 28sqm to, in steps, a final 100sqm, it was found that the added inertia of the heavier rig much reduced their tendency to roll.
Unfortunately, much of how rolling is perceived is very subjective and hence difficult to evaluate.

 

[Blueboatman]

I will add nothing except that it is nice that we are all inveterate tinkerers and practical, thoughtful, hands on ‘improvers’ , and that includes the designers.

Empiricism to the fore!

Now available with computer aided research and measurement ?

Edison, he of the many steps to go through to getting a working lightbulb, would have been proud ..?

 

[Tranona]

In retrospect, my Water Witch had terrible weatherhelm and she wasn't particularly quick either, but she was my first own boat and you rarely forget your first love.

I think that MG was brought up on boats with weather helm and perhaps considered it normal!. Often talked of "relieving lines" and two men on the helm. with the Eventide and the Waterwitch I am sure the flat plate rudder did not help adding a heavy helm to the imbalance that causes weather helm. The two common ways of improving things were a bowsprit to move the jib forward or shortening the foot of the mainsail to reduce the sail area aft. A previous owner had done the latter on mine, meaning a flat leach and no battens.

When I did the underwater mods it was part of a major refit which included new sails. Rob Kemp redid the sail plan, returning the main to the original and a larger furling genoa, taking advantage of the forward shift of the forestay on a stub bowsprit and giving more overlap. The latter was probably a mistake as she was much better balanced with the wind forward of the beam with a couple of rolls in. Overall balance was much improved and even the little Autohelm 1000 could cope in moderate winds. I sailed the boat for over 30 years and still miss it.

 

[Wansworth]

Just as an aside back in 1968 father thought of building an Eventide and that year we had the last family holiday in Teighnmouth and on the vast mud flats on the Shaldon bank were more Eventides than you could shake a stick at(from memory about 12)