BYYB Forums

I got my boat fipped over this last weekend, and am well on my way to having the bottom finished.  My question is I plan on taping my edges with 6"wide tape should I tape before or after the main glassing?  Also how round does the keel need to be.???

I'd tape before glassing the whole bottom and I'd use a 3/4" radius (roughly, unless you want to run along the keel with a 3/4" router bit.)

Mike

If you tape before you sheath, you'll have to fair the taped areas or there will be a hump. Also if you use regular cloth tape, then you're not adding much strength unless it's fairly heavy, so the tape is just additional waterproofing. Given these precursors I'd tape after the sheathing and fair only once, as there would be no benefit to having the tape under the sheathing.

On the other hand, if you use biax tape, you'll actually be imparting some strength. I'd recommend a 45/45 weave and 12 ounce fabric. In fact, if you filleted the inside with thickened epoxy (structural mix) and applied a single layer of 6" wide 45/45 12 oz. biax, then you could have skipped the chine logs altogether without any lose of strength over the mechanically fastened, wooden reinforced chine assembly, plus the weight savings that comes with not using a chine log.

If you 'glass the whole bottom, including the keel, you do as Mike has recommended need to radius the edges. The keel and the chines, plus a "fair body" fillet at the root of the deadwood assembly, so the transition from hull to keel is radiused too. This lets the cloth lay down nicely and saves you much cursing trying to get out wrinkles and puckers. You don't need a 3/4" radius, but 3/8" will be handy.

On the bottom of the keel you want as crisp an edge as you can get away with. The crisper the better in fact. Attaching a shoe could solve this issue handily. I know this seems counter intuitive, but this isn't an air foil like appendage, nor does water flow around it like one. The blunt and crisp, tight corners, actually improve efficiency to a small degree, setting up a boundary layer of water flow, making the keel ever so slightly bigger (in the eyes of the water molecules flowing around it). It's an old technique that is much more effective on a deeper appendage and especially on rudders, but does work here too.

Also as Paul suggested I think a shoe on the keel is a great idea - especially if you sail like me (rocks?  Oh - THOSE rocks).

Mine is a strip of steel that was a pain to put counter-sunk holes into.  I bedded it with roof patch compound but I'm sure there's some expensive "boaty" goop you can use too 

BUT you'll want to find out how wide the available shoe is before rounding off the keel.  I think the original plan to round off the keel was to reduce damage by not having sharp edges on a keel without a shoe.

Hmmm...I didn't know that about the radius on the keel. What about any generated vortices? Better or worse with smaller radii?

As far as glassing over tapes, Paul's right about cloth tape not adding much strength. A bit more ding-resistance at the chine, but that's not really an issue anyway. I'd skip the taping of the chine entirely and avoid any added fairing trouble. Biax fabrics, or triaxial, are really great. Very much more useful for actual strength than cloth, but a good bit heavier and totally unneeded to glass the whole boat. They'd be an added bit of strength at chines, certainly. I don't know if the entire system of fillet/biax/resin would be much weight savings over a stringer, but perhaps; in these boats, I don't think it'd be worth worrying about. We still contend that stringers help fair wavering cuts along panel edges and are therefore worth using for that reason alone, but individual builders choose as they like, of course.

MIke

Mike,  Glass the radius from bottom to keel up about 2" and leave the rest paint .  This will allow water that makes its way in to get out while she is on the trailer.  Many of us can tell real horror stories about glassed keels on these boats.  This laminated design has a short service life in most cases, that or constant maintenance if glassed.   As i recall Peter says not to glass them in the instructions.  8) 8) 8)

The problem most novices have with sheathed surfaces are they have to maintained or you'll have huge issues down the road. I intentionally avoided the deadwood and stem rot horror stories to spare Mike additional concerns. Any time you place a hard plastic coating over a wooden surface, you better keep after it or moisture will get trapped behind the plastic, with limited paths to escape and rot starts, usually unseen until things start falling off.

A reasonable solution is to sheath the hull shell proper, but not the deadwood. This will let the deadwood dry out when it's on the trailer and you'll be less likely to have issues. Of course the hull shell may have issues, but plywood can cope a little better, for a number of reasons. You still want to keep up with dings, nicks and divots, but damage is usually localize in plywood, where solid wood can be a different story.

Yes, "liquid joinery" is far lighter then wooden joinery. By this I mean a taped seam build of a Weekender would be about 30%+ lighter then the batten, chine log and butt block build the plans show. We've got about 40 years of experience with these techniques now, the jury has long since been in and the debate has long been over.

Biax fabrics can be just as light as cloth. I regularly use 6 ounce biax, in both tape and bolt formats. Triax has no useful purpose in home built boats, unless it's a racer and more 'glass then wooden in nature. 45/45 and 90/90 biax are most common, with 45/45 being most used. Biax fabrics would never be used as a sheathing. It is commonly used as a structural element in laminates, but there are no "laminates" in these builds, just some localized reinforcement or abrasion protection. For the curious a single filled layer of 12 ounce 45/45 biax on each side of a butted seam of 1/4" plywood (a typical Payson butt joint), makes it as stiff as a single piece of 3/8" plywood and slightly stronger in tension. The weight difference is considerable if a butt block or other structural element is removed. For example a glue lapstrake canoe is about half the weight of a regular lapstrake canoe, because it has no ribs, no floors, no bands, no stringers, etc. The same is true of the single chine skiffs used here.

Much testing and research has gone into "edges". The crisper the edge, the better the separation on boundary flow layers. The sooner you can dispense these into the main flow, the faster the resistance drops off and eddie making and vortex generation can decrease their affects on the body. Some (including me on occasion) have taken this to extreme by cutting V shaped groves on the trailing edges of appendages to make a better then 90 degree turn, thus a sharper edge and better "cutting" of the eddies.

The edge in play and it's relationship to the body make a difference. For example a planning dinghy would want as crisp a set of chines as it can get, but a hull like Vacationer would want as rounded a set of chines as possible. This is because of flow speed and separation expectations. If you expect flow to separate, a crisp edge will permit a clean separation compared to a well rounded one. This of course is speed dependent. If you can't expect the speed to be sufficient to hope for flow separation, then you shouldn't attempt to promote it, just the opposite, attempt (through shape) to retain "attachment" as long as possible. If the flow remains attached, it's not spilling off, bleeding over or other wise contaminating boundary flow or creating wave making or frictional resistance (within limits). There's an old saying in flow dynamics circles "any flow is good flow". The logic here is you don't want to disturb flow, unless it's an advantage.

When you get into the study of blunt edges, such as square and rectangular mast shapes or bluff cutwaters, such as used here, then a different set of issues arise. Two primarily, the first is high pressure bleed off and second, boundary layer formation on the leading edge.

If a heavy radius is used on the bottom of the deadwood, the pressure bleed off will be greater, because there is less resistance to it laterally. Most of this stuff was rediscovered in the "fence" wars of the early 1980's when the damn Auzzies (kidding) came up her and stole our cup. What was also discovered (actually rediscovered) was that blunt edges can be beneficial at times. A rectangular shaped mast with an attached luff (sail track) is more efficient then a round sectioned mast with the same sail attachment. This surprised the crap out of people, but once studied all made sense.

The same is true of a blunt cutwater. When a square faced mast is presented into the wind, the flow bashes into it's face and pillows out, then flows around. This is why it's so hard to comprehend at first, it's the "barn door" mentality. In reality, the mast doesn't present a square face to the flow, but it offers up a corner! This the ah ha moment if you've been following. The corner separates the flow so the high and low pressure sides of the foil (sail or appendage) now have a neatly sliced flow to work with. This promotes continued attachment and the foil is more efficient over a wider range of incidence.

On the other hand the rounded mast or cutwater doesn't divide the flow as neatly, some billowing and dispersion is introduced, eddies form and the flow separates sooner, decreasing efficiency on the foil.

Does this mean we all should glue a 2x4 to the front of our masts? What about oval and tear drop shaped mast and why haven't I mentioned rotating foils (like laced or hooped sails)? Well, because I'm mean spirited frankly. Actually, it's a much more complex set of variables then I've described, but suffice it to say, you can get round to work better with a few rules, though watering it down to this audience was fun, if not especially complete.

The latest things of interest are scalloped edge leading edges (yes, I typed that correctly). It seems that at certain speeds the foil can be more efficient if it's not smooth, but has big bumps, spaced along the leading edge and on the low pressure side. I've been experimenting with just this theory all summer and at specific S/L ratios, it has merit, but it also can screw the pooch when out of it's operational envelope, so now I'm working on "mitigation" efforts to "soften" the impact on performance.

Okay then, you'll have a written quiz on Friday, so take your books home kids.

Paul,

If I ask you what time it is will your answer include exlanations of; spherical rotation, advantages of atomic time pieces compared to crystal based, instructions on how to build a mechanical time device as well as a comparison of the current time at your location and mine? ;D  Engineers.  :

Actually, I thoroughly enjoy your posts and have learned more from them, and others on this forum, then I ever did in any of the schools I attended.  Now if only any of you could tell me how to get an expresso shot, with a creama head on it, from the machine I bought my wife for her birthday I'll pile up enough brownie points for a trip to a Florida sailing school.  I could use the brush up and come November, or next March, would love some sun and sailing fun.

LMAO,  I was just asking if I should put the 6" wide 9oz strip of fiberglass that I'm using for extra  abrasion resistance on, before or after the main fiberglassing cause I was worried about being able to fair it....lol

You cast your bread on the waters Mike and take what you get ....   8) 8) 8)  Oh ya, put the strips on the top over the sheet.  Wait, what the hell was the question again  ??? ???