25' trailer sailer

Discussion in 'Sailboats' started by LP, Jul 25, 2005.

  1. LP
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    LP Flying Boatman

    Hello fellow boat builders.

    I just thought I'd throw out some thoughts and ideas to everyone and see what bounces back.

    I'm in the process of designing a 25' trailer sailer. I'm using a fairly traditional hull shape combined with modern (epoxy, glass and wood) techniques. The hull is a blend types taken from Chapelle's book "American Small Sailing Craft." The lines are primarily the Casco Bay Hampton boat with an extended forefoot to add lateral area and to lengthen the lwl. The sheer beauty of these traditional types and their inherent seaworthiness make them a great starting point (for me anyways) for a new design.

    Criteria for the design are minimal weight in transit, shallowdraft, moderate to light displacement, siplicity in operation and maybe even a good turn of speed.

    This design would be used for coastal cruising and, hopefully, jumps across the gulfstream for some island cruising.

    Minimal weight in transit equates to a water ballast hull with additional lead as required to bring it to it's lines. I realize I just opened a can of worms, but this is not a TP so I think I'll be alright. ;)

    Shallow draft is self evident, but ramp lauching is the object.

    As far a displacement goes, let's go for "Too big on the trailer and too small in the water."

    Simplicity and speed. Hmmm. How about a cat-ketch with eliptical, fully battened sails. Let's throw in some deck stepped, hinged masts for trailering and ease of rigging and I think we are ready to go.

    I looking for ideas on the mechanics of the water ballast system as it would apply to an epoxy encapsulated strip built hull. Essentially, a large volume of water must enter or leave an enclosed area readily, efficiently and dependably. My feable mind envisions hinged doors that are always below waterline and that hinge inward so that when the craft is heeled, internal pressure seals the door(s). How about an air fitting and pump to pump air into the ballast tank to lighten the craft for trailering. What if's: we forget to open the door(s) for trailering and the ballast becomes trapped, we pressurize the ballast tank and, again, don't release the ballast doors. Maybe I'm going down the wrong road, but I'm interested if anybody has other ideas.

    As far as the rig goes, I like the efficiency of an elliptical sail. The cat-ketch rig allows for two hinged masts the carry the ellipticals. No jib means no effort tacks. Standing rigging would be shrouds on the mizzen, connected to the main by a spring stay and then to the stem by a forstay (I might actually want to fly something up there after all). No shrouds on the main. Should the after mast stand taller than the forward in this case and does it then become the main and do we now have a cat-schooner?

    I'd like to hear ideas and also hear what people think. Maybe even have a little fun with it.

    Looking forward to responses.

    Land locked in Kansas,
    learpilot
     
  2. PAR
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    PAR Yacht Designer/Builder

    One difficulty in using these "traditional" designs and shapes are the displacement for the specific construction method will be considerably heavier then the one you intend to employ. This will require additional ballast, which will require a new rig design. The once comfortable motion of the original yacht may be lost with the higher ballast/disp. ratio, leaving you with a snap rolling beast of other unknown qualities. The other way around is a new design in the "spirit of" the type you'd like to emulate, but with an eye on the requirements of your construction techniques and desires in the craft. It would be a rare design indeed to take a 70 year old carvel carrying a 25% ballast ratio (3/4 inside and 1/4 out) and make her into a well handling speedy craft by today's standards, that doesn't need a reef by Beaufort 4. I can think of many other issues that will need substantial engineering to over come, most ruining the qualities of the original design.
     
  3. LP
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    LP Flying Boatman

    Hull holes and port plates

    Back to the point at hand. I don't mean to disregard your statements. I will give them some thought. I just what to keep the tread on track.

    In a water ballast system, obviously you need a hole in your hull. The questions that arise are, how large of a hole, how much reinforcement is needed around the hull hole, if a hinged portal is used on the hull hole, what are the mechanics of such a mechanism.

    With a wooden hull, would a doubler the same thickness as the hull plank extending half the hull hole (ballast port) width around the port be suitable? Kind of a cold-molded doubler laid on a 45 and 45 orientation. Or maybe, to negate such a local increase in hull thickness, glass cloth in the appropriate dimension and thickness to carry the loads around the ballast port. Then the hull becomes the core material in a FRP system at the port.

    I'm looking at maybe 1000 lbs of water ballast, realistically I think I'm limited to about 850 lbs, due to the hull volume below the cabin sole as my design stands right now. That equates to about 16 cubic feet for the former and 13+ cubic feet for the later. The point being, how big of a port is required for expedient tranfer of ballast. I would lean towards one square foot of opening. Granted, a hinged port would have to be nearly full open to fully utilize the area.

    As far as the port door is concerned, I think either a stainless steel or bronze, 1/8" would be adequate. The hull plank that was removed to make the port could then be mounted to the port plate to fair the hull in the vicinity of the port. Strength requirements for the port plate is the question of how much head pressure must it withstand. Greatest head pressure would occur at, worst case, 90 degrees of heel. Vertical accelerations due wave action should be self canceling since the wave itself is supplying the force of acceleration.(?) With an 8' beam and a port no more that 1 foot off centerline, maximum head would be 5 feet. So, for design purposes, 10 foot of head pressure should be suitable margin. Anybody current on their basic physics? I suspect it's not an issue.

    More later.

    LP
     
    Last edited: Jul 28, 2005
  4. SeaDrive
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    SeaDrive Senior Member

    I think you are tying too hard with your hinged door on the ballast tank(s). A feed tube from a thru hull (with seacock) will do. You will also need an air escape tube (also with seacock/valve). A standard water pump can be fitted to empty most of the water (huff, puff), and the rest drains out.

    Places to find ideas: Nimble Yachts Sea Pearl, water ballasted designs by Jim Yound and Phil Bolger. For that matter, check out the water ballasted boats sold by Catalina and Hunter.
     
  5. LP
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    LP Flying Boatman

    More hull holes

    Thanks for the input. I was thinking that Hunter or Catalina used some sort of plate system. I was initially was looking at a non-powered system for ballast tranfer. A powered system certainly has advantages. I'll have to explore it. Thanks for the insight.

    LP
     
  6. gonzo
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    gonzo Senior Member

    Water bellow the waterline is not ballast. It just lets the boat sink lower in the water. To use it as ballast, you need to install tanks under the deck. Lowering the boat in the water will change the stability characteristics. It may be better or worse depending on the design. Ballast needs to be denser than water. If it is not, you have a neutral or balanced design. A longer forefoot may be a problem. Those boats have a pronounced drag aft. This makes them balanced and well behaved. The centerboard is adequate for lateral resistance.
     
  7. LP
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    LP Flying Boatman

    Gonz,

    I have to disagree with your statement about water below the waterline not being ballast. Perhaps it's a point of technicallity, but any mass added to any area below the waterline and maybe above it that is denser than the substance that it replaces is ballast. While water is not as dense as other substances, it does have mass and it will lower the CG of the craft if it is introduced in the right place. I would be hesitant to add weight under the decks as it would actually raise the CG of the craft. It wasn't stated, but I assume you are talking of moveable ballast that you would shift on each tack. Thats fine as long as nothing fails. In that type of system, mounting the tanks in the turn of the bilge would be more effective since their effect on the vertical CG would be reduce and there would be less foreshortening of the moment arm between the ballast tank and the lateral center of buoyency as the craft heeled. (if you're talking shifting ballast) I know L. F. Herreshoff used planking as ballast in his Meadowlark design. He used exceptionally heavy bottom plank in a shoal draft, modified sharpie design. He used a substance that was lighter than water to lower the CG in that design.

    The designs that I'm using as a starting point for this design have no centerboard. Since I'm going to be building this design, no centerboard means I don't have to build it and ultimately, it's means not having to use a centerboard. I am incorporating drag into the keel. This is a cruising design, so the pronounced forefoot should add to directional stability (and lwl) leaving maneuvering to be done while under power in congested areas.

    As always, I appreciate input and look forward to other points of view and technical expertise.

    LP
    (may the bottle never explode)
     
  8. Jocko
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    Jocko Junior Member

    Suggested sailplan seen elsewhere

    wrt your sailplan, it sounds very much like one used and written about by Chris White - but as a multihuller. His book explains the details, I believe he built the rig himself, if I'm not mistaken. I found a link for the book "THE CRUISING MULTIHULL By Chris White at:

    http://boatbooks.co.nz/multihulls.html

    if it does any good. Good luck. :)
     
  9. LP
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    LP Flying Boatman

    sailplan

    That is very close to what I'm looking at. I'm targeting around 300-350 sq. ft. of sail divided between two masts. I haven't run the numbers yet, but I'm looking to maintain a decent aspect ratio and keep the CE as low as possible.

    LP
     
  10. gonzo
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    gonzo Senior Member

    Water will lower the CG. However, a design that needs ballast for stabilty won't handle well without it. Hampton boats carried a considerable amount of rock ballast. As for the forefoot giving directional stability, that may not be so. A sharp forefoot makes a boat tend to broach, the opposite of directional stability.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Water ballast isn't a good idea for a cruising boat, especially as you envision it. Water makes a very poor form of ballast (it takes up way too much room and moves around) It only is useful if used to lighten trailering loads or to increase the righting arm like that used in racers (though this fad is fading) Some production craft do use it to lighten the trailering load, but frankly the amount of water taken on by these boats can easily be handled by a small pickup, SUV or mid sized car if it was replaced with a solid material. In these boats, I believe it was more a marketing ploy to emulate the latest racing trend, more so then to decrease trailering duties.

    I think what Gonzo was referring to is the free surface of liquids effect. The shift in the center of gravity will always be unfavorable in the system as you have suggested, because the water will run to the side that is heeling. This is why bilge tanks and pressurized systems are used in racers, to take advantage of the movable weight, placing in on the windward bilge. Even baffled tanks that are full will have a negative effect on the CG, not as much as a bilge half full of water, but a measurable effect in any case. If your keel was hollow and the water contained within it, you could use it to reasonable effect, but if athwartship tanked in the bilge, not so much.

    LFH's Meadowlark design was an uncommonly light design of very shallow draft, limiting the ballast options available to him, so typical of the era, he used progressively lighter dimensioned planking stock, moving from the garboard to the sheer strake. This was a common practice and still enjoys favor in several construction methods.

    There's been considerable historical development of the Casco Bay Hampton boat and it became quite extreme eventually, ruining the type. The forefoot was deep. I don't understand the logic of increasing it further, unless you want a Dhow, which is an interesting craft, but tests and development have proven the concepts have less advantage then other, more widely accepted techniques to gain maneuverability and good tracking in shoal craft. These craft were also quite burdened by there trades and their shapes. The concept of pivoting on the bow and raised quarters has been proven inferior by many designs over the last couple hundred years.

    Have you any sketches of your proposed modifications to the lines of these vessels?
     
  12. LP
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    LP Flying Boatman

    PAR,

    Here is a screen shot of the lines as they stand. The sail plan is tentative. I reviewed my resources and found I was making reference to a different craft. I liked the comments that Chapelle had about the sailing qualities of the Toulinguet boat. It has the raking stem. My lines follow the Casco Bay craft fairly closely. Sorry for the confusion.

    I'm still not quite ready to give up on the water ballast idea. The issues you present are volume and sloshing. My intention was to create a ballast tank under the cabin sole. Historically, a place that collects water anyways.
    :D So, why not make the cabin sole the pressure bulkhead and have every cubic inch of volume below the cabin sole used to capture ballast. I see some secondary advantages to such a system. First, the cabin sole then reinforces the hull at approximately the waterline. Slightly below it in fact. Should a person encounter a floating or submerged object, where else would you want reinforcement. Should your encounter breach the hull, it would be of no consequence. You're already full of water below the waterline. The pressure vessel is still intact. Second, my intent is to always sail with a full ballast tank. I only mentioned bilge tanks earlier to expand on a point. Granted there may be a small volume of air that does not evacuate when filling the ballast. I see that as a design issue. Something as simple as a cabin sole that inclines to the bow with an air vent in the area of the stem. A third point would be that since water is neutrally buoyant in water, if a person wanted to make the vessel positively bouyant when swamped, there would be less of a volume required for floation material.

    I'll willing to admit that water in not the best material for ballast. In fact, it's a compromise at best. But that is what boat design is all about. In this day of $2+ a gallon gasoline, that 800-1000 pounds of water ballast looks pretty good. Thats a 25-30% reduction in trailer weight.

    Actually, all off this discussion has led me to a very simple system for ballasting, that should the idea of water ballast fail, there will not be a large investment in time of materials. Invision this. Ports not in the hull, but in the keel throught the deadwood. The deadwood would never leave the water unless on the trailer so by essentially stuffing a "cork" in the air vent located at the bow, the ballast is trapped by one simple devise. Attach an air pump to the vent and you can evacuate the ballast in preparation for trailering. Should the whole thing fail, plug all of the vents and ports, bolt on the additional lead and be on your merry way.

    As always, I'm open to input. Keep sending me posts. I'm obviously inexperienced at boat design and probably am viewing it though rose colored glasses.

    LP
     

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  13. gonzo
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    gonzo Senior Member

    It seems, at first sight, that the center of floatation is well aft. Without a great deal of ballast aft it will float down by the bow. Water won't do it. This design was supposed to have a bunch of rocks in the deep bilges aft. You flattened the run so there is no place to put ballast unless it is exterior. Boats that use flooding water tanks are rather flat in the bottom and have balanced displacement fore and aft.
     
  14. LP
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    LP Flying Boatman

    Gonzo,

    If you look at the lines, yes, the entry is very fine. I like it that way. If you were to rake the stem and shorten the waterline by a foot or more and redraw the waterline to that point, I think you'll find that the center of buoyancy is not so far aft, compared with other models. There is also a fair amount of flam in the forward sections. So, as the bow pitches down, reserve buoyancy comes into play. The interesting thing about filling the bilge with water ballast, is that the ballast distribution matches the displacement/buoyancy distribution. The water ballast in this design is part of the ballast equation. Additional conventional ballast will be added to bring the vessel to its lines.

    Let's talk about the mechanics of water ballasting. In a moment of clear thinking (or clouded depending on you point of view), I saw, say, a half dozen 1" holes penetrating the center of the keel and/or deadwood. Just for grins, let's line them with copper to kept the critters at bay. Then at the bow, we'll have an air vent leading to topsides or perhaps to inside the chain locker. This vent will have a valve for control of entry and exit of ballast (or air, again depending on your point of view.). Maybe, there will be a second vent aft, just in case the bow sinks. (or something) All other thoughts aside what would be the inequities in such a system. An addition of an air pump connected to a vent pipe would aid in evacuating the bilge in preparation for trailering.

    LP
     

  15. capt'n ron
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    capt'n ron Junior Member

    if a rookie might add a thought?... every thing i've read so far makes me agree with PAR. alrhough water is ballast, as any amount of wieght below the c/g will enhance the pendulum. the lower the better. water, i will agree is a "not so good" a ballast in the case of a boat of this size, it just isn't heavy enough and takes up too much room to be effective.i think the real evaluation here is the height of ballast volume. rocks, lead, even concrete is many times more dense than water so it will take up space that is lower in the boat in volumetric comparison to water, a major consideration in the effectiveness of the ballast.
     
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