Help with Design Modifications

Speaking of materials in general and cardboard in particular, has anyone worked with 'plascore'? A guy on another board pointed it out to me and said it was very reasonably priced, cheaper than plywood. I presume it takes much more glass and resin in the layup compared to wood, but I think that cored boats last and are valued much higher in resale than plywood because they don't have the swelling and rot problems. I suspect it is not as stiff as more expensive cores, but I also think it would make a very nice light forgiving hull. And it can be thermoformed to make shapes that won't oilcan.

Regarding cheap experimental sail material for small boats, I like polyethylene tarp from the hardware store and fiber reinforced packing tape. If you look at the expensive carbon and aramid tape drive sails as a guide you will know just where to run the reinforcement. In addition to transparency, it is very forgiving, repairable, and from a distance it looks 'pricey custom' not 'cheap dumpster diggin's'.

 

I have not seen that, it would be interesting to get a price for buying a few sheets at a time. I have seen a similar product made of cardboard that is about 1/2" thick that I wanted to play around with making frames for a corrugated cardboard kayak, but it cost more than 1/2" CDX plywood (about $40 for a 4x8 sheet vs. about $22 for plywood), so I saw no point in using it.

 

Plascore is a honey comb material, but needs a considerable amount of laminate to become a stiff, self supporting and strong panel. Once you count the resin and fabric costs, you're way above the cost of plywood.

 

If I had any real idea what wing sails were all about, I probably would. Living so near the modern home of private aviation (Mojave, CA), I've already toyed with the idea of making a cardboard airplane. So, if a "wing sail" is what it sounds like - a vertical airfoil - I'm sure I could do it.

Well, the other problem is that my only exposure to wing sails is a few ugly pictures in Sail magazine of wing equipped boats capsizing.

I realized today that one of the storage containers in the back of my school has two rolls of that black polyethylene sheeting that gardeners and landscapers use. WIll that work? I'm sure no one would notice if I cut a few feet off for experimental purposes, but if anyone asks I could say I'm using it for "Professional Development," so I can master new concepts for my Physics & Technology class.

 

Small Boat, Big Water

When considering a small boat design, say, under 20ft in Length and half a ton in displacement, for use in open water, there are trade offs that simply don't apply to larger boats.

These are:

1.) range of stability vs. high initial stability,
2.) water tightness, on top, vs. low Vertical Center of Gravity (VCG), and
3.) access to sails and control surfaces vs. Longitudinal Center of Gravity (LCG)

There is a handful of designers who have taken on these trade offs. Most you may not have heard of. These designers have built and sailed their own boats.

The ones I know of are: Sven Lunden, Matt Leydon, John Longyear, and, another favorite of mine, Phil Bolger.

Starting off with the first trade off.

Sail carrying ability, what you need to sail upwind , punching through a chop, comes from high initial stability. In smaller boats, this usually comes from the skipper, usually the heaviest item on board, placing his weight as far to windward of the boat's center line as possible. This usually means his weight is carried quite high on the boat, at the sheer, or even higher.

This imparts great initial stability, but comes at the cost of a dramatically reduced range of stability. The higher the sides of the boat, in relation to it's Beam, the more true this is. In a sudden, severe knock down, of say 80 deg or more, the skippers weight, which was keeping the boat upright, now becomes additional capsize moment. The boat is then all but doomed to capsize.

But, putting the skipper lower in the boat, usually means he cannot put his weight far enough to windward of the center line, to impart much initial stability.

This brings us to the second trade off.

In order to move the skipper's weight far enough from the center line, yet keep his weight low in the boat, the side decks must be very low, in relation to the Beam. Or they must be removed altogether. On a high sided boat, this means the cockpit seats must be quite low, in relation to the side height, as well.

A multihull is an excellent solution to this dilemma, as its outer hulls can be completely decked over, and its side height to Beam ratio is quite low. It has almost exclusively initial stability, but such is so large that the skipper needs only to use a portion of it to get adequate driving power. Also, the lee hull can have enough buoyancy, so it cannot be submerged. Such is often not the case with a low sided, decked over monohull.

A mono hull solution to this dilemma, is to make the boat so easy to drive, that it doesn't need much initial stability. Making the boat long, in relation to its Beam, is one way to do this. Such a boat can have quite high sides, as, due to its sectional area being width times height, its small Beam keeps such area low. Matt Leydon's 'Paradox' is an excellent example of this strategy, as is Phil Bolger's 'Bird Watcher'. Matt's boat is only 14 ft long and has tackled open water successfully. Such a boat needs a short rig, in relation to both its length and Beam, and may not be the hottest performer.

But, what if you have to go forward to take the jib in, or aft to work on the rudder?

This brings us to the third trade off.

A skipper, on a small boat, has what I call the king Kong effect. Imagine King Kong, a fifty foot tall ape, on a small harbor tugboat. If he goes too far aft, the stern goes under. If he goes too far forward, the bow goes under. If he is too high up in the boat, maybe even on deck, the boat capsizes.

For this reason, the skipper must be kept away from the extreme ends of the boat. The jib, if the boat has one, must have a roller furling system or a down haul, so the skipper can raise and lower it remotely, especially in wild conditions. Such systems must be incredibly reliable. I prefer a down haul, and will not own a boat, with a jib and no roller furling system, without one.

Since the skipper is usually the heaviest, or second heaviest, item on board, his weight should be kept as close to the center length of the boat as possible. The longer the boat is in proportion to its Beam, the more true this is. It may not be possible to steer such a boat with a conventional tiller, as the skippers weight must be kept so far forward of it. A steering line, or a yoke system should be set up. It should be much stronger than the typical loads put on it, so there is no doubt at all that it will not break. The same goes for the rudder and rudder hinge assembly. If the rudder has a drop down blade, it should be able to be raised and lowered without the skipper hovering over it.

In the attached drawing, is a design of mine, which, although an extreme example, follows most of the principles mentioned above. It has no jib. The mast is placed close to where the skipper sits, so he can easily raise and lower the sail. It has a continuous steering line. And the swing down rudder blade has a bungi cord to pull it down, and a line, leading to the end of the tiller, to pull it back up.

As an alternative, a boat can have a wide stern and have its center of buoyancy far enough aft that the skipper can sit in easy reach of the tiller. This is a very popular approach. And for good reasons. The wide stern also accommodates an outboard engine, something you should really consider having, for your Catalina voyage.

For the sake of argument, I would make the following changes to the 'Blue Moon' design:

1.)I would replace the centerboard with a keel that was 8 ft long, that would extend about 1.0 ft deep, and would be about 3 inches wide, and be about two hundred pounds in total weight. The ballast slug would be made of concrete mixed with rebar and steel punchings,
2.) I would extend the rudder depth to just short of that of the keel,
3.) I would shorten the cockpit. Extending the aft deck to the end of the tiller,and put a water tight bulkhead there,
4.) I would put a hatch in the foredeck, so I could remove the jib without going out on the deck,
5.) I would put flotation in the bow, extending down from the deck to the keelson there, extending about a foot and a half aft, and
6.)I would have a down haul for the jib and one deep reef for the mainsail.

I would also consider cutting an outboard well, so I could get to the outboard engine without going so far aft.

After I was done with all these changes, the boat, above the waterline, would look pretty much the same as before.

 

If you are still interested in PDR type boat building, have a read though a couple of the threads by Steve Lewis on this site. Im always impressed by the simplicity of his builds. He has demonstrated a side of boatbuilding and sailing that could be accessable to anyone no matter how tight their budget.


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