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  #1  
Old 02-25-2004
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fast displacement hull?

So all of the race boats are essencialy surf boards with a cuddy cabin and a big set of sails. alot of the smaller boats I''ve seen are starting to duplicate this trend.
This makes for rather.. short accomidations below, or hunter-esq amounts of freeboard.

Older boats, Vertues and hess designs etc, and even some of the CCA boats I''ve seen may be only 25'' long, but still have sometimes 4 or 5'' draft (and resulting 6'' headroom)

I''ve seen boats that claim to be fast despite this, and it seems odd due to the exponential increase in wetted surface area.

Anyway, is this realistic, given a properly designed hull, with a fine entry, could still be "fast" which is to say, sail at the same or similar level as a boat of similar displacement that caried its weight across a larger beam and less depth of hull (keel depth notwithstanding) with similar sail area, etc.

Pros, cons of this design? Any good examples?

Thanks.

-- James
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Old 02-25-2004
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fast displacement hull?

James, You do have a way of asking questions that beg complex answers. First of all, I think that it is an over simplification to say "all of the race boats are essencialy surf boards with a cuddy cabin and a big set of sails. " While many of the more extreme small race boats are essentially high performance planning boats with little accomodations (Melges 24 being the poster child for that description) there are a lot of variations out there and many do offer reasonable accomodations. Most that fall into the higher performance racer cruisers are IMS type forms (the Beneteau 36.7 and C&C 99 are good examples of that type). These boats are not planning hulls like the smaller higher performance dedicated raceboats. Instead they are more typically semi-planning hulls with moderate sail plans. These semi-displacement hulls are not especially beamy. They do have shallower hull forms because they are lighter in weight than the earlier designs and generally have less wetted surface and more easily driven hulls permitting them to use more efficient sail plans. The newer racer-cruisers also tend to have a larger proportion of their weight in ballast with the ballast placed more effectively than on older designs. As a result of less wetted surface, more easily driven hulls, more efficient sail plans and keels, and more stability, they get a lot more out of the sail plans.

While boats like the Vertues, and older MORC some older CCA era boats have been described as fast, that is only relative to other boats of that era. The reality is that in any objective sense, the newer designs tend to be faster on all points of sail and all windspeeds. Newer designs have thier greatest speed advantage at either end of the wind scale.

While it would be possible to design a boat that had many of the virtues of older designs but which was optimized based onthe lessons learned in the past 25 years about speed and seaworthiness, that boat would in fact give up some performance to the newer boats that are solely optimized for speed.

That is not necessarily a bad thing. When I decided the buy the boat that I did I wrestled with this very same set of compromises. I did not want the draft restrictions of the latest generation of race boats and I wanted a simpler and more robust rig than is found on modern raceboats. I knew that I was giving up substantial performance over a brand new design. Comparing the PHRF rating of my boat at 87 to a newer Farr designed Beneteau 40.7 at 51 this is not an insignificant compromise but for my purposes, and budget this made much more sense.

Boats are a system. There is no point to designing a boat that is a semi-displacement hull and then strapping it with the high drag of a full keel for example. With the full keel, the need for more sail are arises. With more sail area more ballast is needed. With more ballast and sail area the structure of the boat needs to be beefed up. And with all of that added weight, it gets hard to produce a semi-displacement design with all of its advantages in terms of speed and ease of handling.


These are the very issues that I have been wrestling with lately as I have been messing around with the design for a small daysailor/gunkholer/weekender that I am thinking of building for myself. Again I am considering compromises in speed to gain a bit more room down below and the ability to duck into backwaters.

All boats are a compromise. There is no one right answer here.

Jeff
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Old 02-27-2004
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fast displacement hull?

James, let me try to restate your question in order to help clarify my answer: I think you are essentially asking if, despite or perhaps because of the current, predominant ''go-fast'' designs you see among smaller sailboats, is it reasonable to assume one can find a smaller boat that is a different, newer kind of compromise? You mention characteristics that might blend the ''old'' with the ''new'' e.g. the contemporary trend of a fine entry, abundant beam (and I''d add, a semi-balanced rudder) with perhaps the deep keel and higher B/D ratio found in older designs like the Virtue.

Conceptually, the answer is of course ''Yes'' since yacht design, manufacturing techniques and construction materials all evolve over time, as do our expectations and requirements as potential customers. On a less theoretical level, I think what''s happening here (in the UK) right now with the introduction of the Sadler 29 is an interesting example of exactly what you are asking about. A bit of history: the designer produced a 38'' design three years ago that Hunter Boats (not the U.S. Hunter) introduced as the Mystery 38 roughly 18 months ago. It embodied many of the ''old'' characteristics - longish overhangs, narrow beam, and even a tiller - and in fact that was Hunter''s intention: to revisit older design characteristics that produced nice sailing boats, but to add in modern construction techniques (nothing radical nor costly) that would improve even further on the results. It''s getting huge praise for its sailing qualities (not just speed but also handling and ''feel'') but gets disappointing comments - surprise, surprise - about its smaller cabins and unHunteresque interior appointments. (I like that term...).

Meanwhile, the tradename ''Sadler'' is being reintroduced here - it has a very positive connotation due to its many ''good sailing'', affordable sloops built in the 70''s & 80''s, which are sought after actively here. The new builder went to the designer of the Mystery 38, in part because of the results from his Hunter design, and the result is about what you described: a Sadler 29 that is full of beam, with a quite fine entry, and with a emphasis placed on both a large B/D ratio AND locating the ballast relatively deeply (off composite ''spacers''). Especially noteworthy was the part of the design brief that said the boat would be offered as either a fin keel or bilge keel hull BUT it needed to be fast to weather with little leeway regardless of which keel was chosen (altho'' obviously the fin will be more effective). The boat (with bilge keels) does up to 7 kts on a beat (as independently tested on multiple occasions in varying wind strengths on the Solent), is every bit as impressive in cabins, space and finish as any Scandinavian or French product, and - one of the things I like best - comes with a tiller, only too appropriate on a boat of this size & displacement with a design brief to be sailed fast.

Here''s the punch line: the boat has some of the same design parameters as the larger Mystery 38: LWL, beam, SA/D and B/D ratios. Or put somewhat differently, the designer took too different design briefs that shared some common goals (nice sailing ''feel'', fast, stable and with excellent ultimate stability) and applied some of the same design techniques & approaches to them while producing boats that, in other respects would seem to be quite different (''traditional'' vs. modern; larger vs. smaller). Neither design relied on particularly high-tech (or expensive) production methods. In fact, Hunter is known for its Hunteresque prices while Sadler, a start-up, couldn''t afford those initial production costs.

Perhaps I''m guilty of a wee bit of hyperbole, but one of the ways I''d sum up these unfolding events is that the the importance of a skilled designer - when designing both a sailboat that sails and a comfortable cabin - is being re-emphasized in these boats despite the high-tech emphasis of other new (racing) boats and the high-volume production cost efficiencies of the huge manufacturers. To the extent this is a fair observation, I quite like this development...

Jack
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Old 02-27-2004
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fast displacement hull?

Jack, as I read your answer and went back to look at Jim''s original question, I decided that I am not really sure that I understand what Jim was originally asking.

I took the question to mean, "Can you produce a design for a small boat (25 feet or so) with modern performance but with a long keel and decent accomodations?" I would say, probably not, meaning that to add the additional weight of an interior and drag of a long keel, then the speed advantage of a modern semi-displacement type would be compromised to one degree or another. I tried to say that that is not necessarily all that bad a thing because all boats are a compromize and it is not the end of the world to give up a bit of performance to gain nicer accomodations. (I don''t see any good reason to go to a long keel on a modern hull form except nostalgia but that is just my own taste.)

There is another factor at work here, which is one that I have discussed many times here. In order to go cruising, a certain amount of displacement is needed per person. I have generally tossed around the traditional 2.5 to 5 long tons per person found in classic cruising literature. If you size a boat by displacement (rather than by length), which is something that I strongly advocate, modern designs tend to be longer for their displacement. Jim mentions the Vertues, which were roughly 8,500 lb 26 footers. If you were going to build a modern 8,500 lb cruising boat, it would probably be somewhere around 32 feet long. In theory it would be no more expensive to build or operate than the 26 foot Vertue (dockage not withstanding) but would offer enormously faster performance on all points of sail and in all conditions(probably on the order of 2 or 3 minutes a mile). In theory the newer design would be easier to handle and would offer similar or better seaworthiness and motion comfort, and a lot more physical space down below but would not have that much more carrying capacity than the Vertue.

I think the question also seemed to be asking, ''Can Jim find a modern 26 foot semi-displacement type design with all of the accomodations and capacities as the Vertue?'', and the answer probably would be ''No'', because the modern 26 footer would have a displacement less than half of that of the Vertue.

But I am not sure that is exactly answering the question that Jim is asking.

Jeff
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fast displacement hull?

JeffH wrote: "...If you were going to build a modern 8,500 lb cruising boat, it would probably be somewhere around 32 feet long. In theory it would be no more expensive to build or operate than the 26 foot Vertue (dockage not withstanding) but would offer enormously faster performance on all points of sail and in all conditions(probably on the order of 2 or 3 minutes a mile). In theory the newer design would be easier to handle and would offer similar or better seaworthiness and motion comfort, and a lot more physical space down below but would not have that much more carrying capacity than the Vertue..."

This is exactly the point I have been trying to make, unsuccessfully, on another BB. The consensus there seemed to be that boats of equal displacment have near equal belowdecks space.

I suppose that argument may have some merit when comparing boats of very similar design and construction, but certainly fails when comparing very dissimilar boats such as Jeff uses in his theoretical analysis.

Duane
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Duane, that BB''s view fails in several dimensions. E.g. imagine a 30'' cored glass sloop and a 30'' steel sloop...or a 30'' traditionally-built wood sloop, all built to a similar high standard.

Perhaps you need to make your point a different way: compare apples to apples by looking at two wooden planing-hull powerboats. Using the strip-planking method (augmented with kevlar cord & epoxy), Cutts & Case on MD''s Eastern Shore built a 42'' planing powerboat hull that weighed in at <5,000#. And with similar savings in deck weight, the boat needs a smaller engine to reach planing speeds (less weight) which will in turn burn less fuel, making smaller tanks possible (less weight). The hull shape was conventional and could be directly compared to the (twice as heavy, as I recall) conventionally built wood hull, so...same lines, same building material (sorta...), same intended use, and same interior room but with a much smaller displacement.

Jack
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fast displacement hull?

Jeff:

Actually, I restated Jim''s question as I thought I understood it because I wasn''t sure...

"I don''t see any good reason to go to a long keel on a modern hull form except nostalgia but that is just my own taste."
I think it''s more than ''taste''. You are thinking in terms of your own waters & locale, and even if it''s subconscious, when you contemplate a design I''m betting it''s with certain assumptions about facilities, tides, etc. "built in". In Europe, where scrubbing stands are funded by ''local authority'' as they like to say, and where the cost of boating is much higher relative to the level of income, something like ''taking the shore'' using bilge keels or using a scrubbing stand with a clear conscience because you have at the least an extended fin are considered ''normal preferences''. Were you here - and based on me reading between the lines in some of your posts - you might find yourself challenged by sheer creativity to think in very different terms WRT your design preferences. But that''s just idle speculation on my part on a cold, grey afternoon...<g>

Jack

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fast displacement hull?

Thanks, Jack, for that added "ammunition."

Cheers,

Duane
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Jack,

I understand your point that long keels have certain practical aspects that make them compelling for some applications, but when you look at modern IMS typeforms, they count on being low drag underbodies in order to make some of the gains in motion comfort and speed. It is a bit of a non-sequetor to add the high drag of a long keel or bilge keels to a modern hull. If you want a long keel then it makes more sense at that point to stick with the virtues of a traditional hull since you will reap few if any gains of a more modern hull form.

Jeff
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Jeff, I don''t think I ever suggested a long keel as a preferred or even suitable choice, even in waters with substantially different demands.

As for the bilge keel option, its attractiveness is a function of certain unique conditions, as you know: 15-20'' tides coupled with conjested anchorages and mooring fields in season, and often narrow estuaries that limit one''s exploring every tide cycle. So...it''s as tho'' the design criteria expand if those needs need to be considered (which for many people here, is the case), at which point speed and comfort requirements must be augmented with concern about the water in which the boat is used.

As I mentioned earlier, I think the Sadler 29 is shaping up to be one of those breakthrough designs where a conventional choice (at least insofar as the bilge keel model is concerned) provides more performance than thought possible. And it has many of the attributes you have described as more modern and beneficial.

For the budget-minded Brit or Scott, Belgium or Irish sailor, taking a grid becomes very important; I''m sure the same must be true in N France and the Channel Is. and the Dutch sailor has a huge inland sea that makes taking the ground a common occurrence. It will be interesting to see what this means in those locations relative to keel preferences but the modern short-chord keel is a worrying choice if one must dry out the boat for a scrub or in order to remain at a wall in a drying harbor. Even ''legs'', still carried by some boats, require an extended fin.

Jack
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