: Hi Folks

: Someone skoot over and give me room to sit on the porch here for a spell and
: cast off some ideas and questions and see what'all bites. . .

: I'll be building three skin boats from the direction of Mark Starr and Robert
: Morris' books ( 'cause those are the only two I have at the moment ) and
: after seeing many completed boats, in both styles and reportedly built,
: for the most part, with anthropomorphic measurements, I've got a question
: about this style of sizing.

Go get another book. George Putz's. You'll appreciate how he captures your laid-back authorship. Oh, and the word you want is anthropometric, which refers to measurementa taken from a human, rather than anthropomorphic which means the boat resembles a human form.

: Most of the boats I've seen pictures of, in progress and finished, seem to be
: of high volume and MUCH freeboard when in the water being paddled. A
: couple have complained of this and some enjoyed it and for the most part,
: all have been happy with their boats.

I always thought the high freeboard was because the boats were built for men with your physique, but the pictures were taken while these boats were paddled by waif-like models who weighed far less than the designweight. For the record, I'm among those who enjoy it.

: . . . It appears to me that there is a
: great difference in the boats built by the Greenlanders and the boats
: built by those using the books as direction.

My long held belief is that an anthropometric measuring system may be accurate within a fairly narrow range, and that's it. At as the paddler size deviates from the center of that ideal range the system should fall apart. Either that, or you will find that there are many compensatory rules added to make the system work. At some point it should become obvious that you are substituting inaccurate measurements for a ruler, but that they are within a certain margin of error, or merely coincidence.

This would follow the same line of reasoning we've seen in other areas. For example a person who grows out of their jeans and has to go from a size 34 waist and 30 leg to a size 38 waist does not necessarily need a pair of pants with a 34 inch inseam.

Or maybe this analogy will be more appropriate: If you are happy with your cookies (and many are!) but you want to make a cookie which is twice as big as what you are usually making, you don't need to double the baking time, or the oven temperature -- and you certainly don't need to double BOTH! Certainly some adjustments must be made, though.

: I'm not saying the books are incorrect, as the boats I see on the Qajaq site
: and the boats pictured in the books all look like low volume boats and
: those I see being built by most on the KBB turn out to be of rather high
: volume and much freeboard. Something seems amiss here. ???

My thoughts are that as the boats are built for larger paddlers the multiplication gets out of hand: The volume grows as a cube of a measurement, whle the length and width grow as a square of some measurement. Again, the anthropometric sizing may be perfect in a certain range, but following the "rules" too rigidly will lead you astray.

: Is this something that has to be figured out with formulas, design, or are
: some of the builders taking other measures to keep their boats low volume
: and less freeboard??

Well, yes and no. The formulas can be fairly simple, and they can also be complex. epends on what formuals you want

Design is always a consideration. You need to have some idea of what you are building before you start.

: I'm interested in building a boat that's much lower in freeboard, more for
: play and short trips and am not interested in long camping trips and
: barge-like boats.

OK, then build just that. If the way you measure yourself, and apply those measurements to these plans, calls for a high side height, then change it. Make the side height and freeboard as small as you like. Even if you make the boat only 2 inches high it should float like a surfboard. Or, if it sinks it will go only so deep, until enough of your body is underwater to match your weight with the weight of whatever water was displaced.

Of course if you calculate the displacement you can avoid getting wet

: An example of what I'm talking about would be that designed boats, from most
: of the commercial sites, for my weight and height, all seem to point to a
: 17-17 1/2' boat with a 23" beam. While I'm coming up with the same
: beam, using the anthropomorphic measureing method, my length is scooting
: up to the 19 - 19' 4" length. This seems to be spelling BARGE and 5
: to 8" of freeboard to me. NOT!!!

I agree. and I've said why before. If the system is not good for you then don't stick with it. It may be perfect for someone else, though.

: I've already built one boat using other's ideas and it came out too large and
: for the most part unusable for me alone.

OK, now here is the crux of the matter: You have all the data you need already, and you did not share it with us: HOW BIG WAS THE FIRST BOAT? Tell me that and how high it floated above the water (the freeboard) and I can tell you all you need to know about the design of your skin-on-frame boats. Or better yet, I'll tell you how to figure this out for yourself a little further down.

: Where does weight factor into these equations??

Weight of you, plus the boat plus your gear is the primary factor in determining the size of your boat. The width of your hips and butt, and your desire for comfort will determine the width. The boat can't be any narrower than the seat you sit in. It can be wider if you wish. The length can then be adjusted to give you the desired displacement. And then you can tweek things like rocker, bow height, symetrical, fish- or swede-form, etc. to give you the handling characteristics you want.

BUT, if you have already found a boat that you have some history with, then you are well on your way to getting a boat that meets your expectations. Don't start from scratch with your body, but work from the experience with the previous boat. If the first boat floated too high you can make it narrower or shorter. Doing either will reduce the boats volume and let it sink deeper in the water, which will lower your center of gravity and give you more stability. By pulling more of the boat underwater you also reduce your freeboard. If you want more maneuverability, chop the length. If you want better speed and tracking, reduce the width.

: . . . I mean, I'm 6'3" tall
: and 245 lbs, and my reach is 76" from tip to tip. I'm sure there are
: others that have the height and reach, but are lighter or heavier. So,
: this is critical to the volume and how does it figure into the skin boats
: design?? How do I know ahead of time just how tall to make the boat for
: the proper freeboard. Is it all guess work..... build and take what you
: get???

No, it is certainly not all guess work -- although educated guesses have orked fairly well for a lot of people for a long time. Now we have computer software which can do the math necessary to give you an exact volume and displacement of the curved, submerged surface of the hull. It replaces a lot of calculus.

If you are not starting completely from scratch, though, your need for calculus is greatly dimminished. You don't have to redefine curved shapes, you just have to measure a boat that works for you, and build your s-o-f to the same specs. Or modify the specs of a boat that doesn't work for you.

Here is how I do the math. First, I assume the boat is symetrical and made of straight, not curved lines. A kayak then becomes a long skinny diamond shape. Cut it in half and you have a triangle. the area of the triangle is half of its height times it's width. Since I have TWO triangles, I just measure the height of one triangle and multiply it by the width.

Or in other words, I take half the length of the kayak and multiply it by the beam to get the area of the "footprint" the boat makes in the water.

To make this real simple, lets use the example of a 16 foot long and 24 inch wide kayak. half the length is 8 feet, and the width is 2 feet. The area of this boat's foot print is 16 square feet. If the boat had sides which were high enough, you could sink it a foot into the water and it would displace 16 cubic feet of water. A more reasonable idea is to sink it 3 inches, or a quarter of a foot, which would give yo a total displacement of 4 cubic feet.

I "ballpark" the weight of water at 60 pounds per cubic foot. So 4 cubic feet of water would weigh about 240 pounds. Thats how much a 16 foot long by 24 inch wide kayak with straight sides and a flat bottom will displace when submerged 3 inches. If you reduce the width to 23 inches your width and area change by 1/24th of our example. So would your displacement. So, drop an inch from the width and our example would reduce by 10 pounds (1/24th of 240 is 10) The displacement would be 230 pounds.

maybe you can already see the pattern here. With a slabsided, flatbottomed 16 foot kayak with a 3 inch "waterline" displacement, the amount of displacement in pounds is simply 10 times the width in inches. A 20 inch width would displace 200 pounds, and a 12 inch width would displace 120 pounds.

since the boat is sinking 3 inches for these values, any change of an inch will alter teh displacement by 1/3rd of these numbers. For a 4 inch displacement, on our original 24 inch wide example, the weight of the water displaced would be 320 pounds. or, you could multiply any width in inches by 13-1/3.

So, to get the displacement value for any additional inches of immersion, multiply by the width of the boat in inches by the desired draft in inches times 3.33333.

Now nobody builds a boat like that, and I would not suggest anyone bother to, either, so there ware going to be a lot of questions as to why I bother with this estimating. Well, If I can sit on the porch with you and grab a cookie, I'll tell you.

Once the rounded bottom of a stripper, or the v-shaped bottom of a plywood or skinned boat are submerged all that is left to sbmerge is the sides -- and the closer they approach straight lines the closer they approach the above estimate.

So, I pretty much ignore the volume taken up by the first inch the boat submerges. Or I give it half the value. So, If I want to get an estimate on the displacement of a boat I fudge the value for the bottom and just worry about the value I can figure for the sides. In this case, with a draft of 4 inches a typical 16 foot long and 24 inch wide kayak would probably have a displacement close to my calculations for 3 inches plus a half an inch or 240 pounds plus 40 pounds, or about 280 pounds.

Rehd, in a 16 foot boat with a 24 inch beam which weighs 40 pounds you should fit and have a draft of about 4 inches. Then, for every additional 10 pounds of gear you should sink another 1/8th inch, which is trivial. If you made the boat 23 inches wide, then your draft would be about 4-1/8th inches, as you lose the 10 pounds of displacement when you narrow the beam.

If you want to have 4 inches of freeboard, make the boat only 8 inches high. That may be a tight fit for your feet, so you can make the front deck higher than the back one. either do this for the whole length, or make a raised area just over where your feet are by using higher hoops near there.

If you want to have a low back to your cockpit, sit on the seat you'll use in the kayak and measure from the bottom of that seat to the small of your back (probably around 8 inches) and that is how high you want your coaming to go.

Now, how big was that "double" you built? use the above "formula" to figure out how much "displacement" it had, and then play with the numbers to reduce that down to where you are riding lower in the water, and have less freeboard.

: I want a boat to play in and the next one will be it.

: I'm buiding two smaller
: boats for my grandkids in the 12 - 13' range, and one for myself as well (
: length undetermined as of yet ). All this winter and all S o F. I already
: have plans for a Merganser 17w for the spring and hopefully done by the
: R2K3 meet.

OK, now you may wnat ot reconsider your choices for what you will be building, or modify the designs a bit to adjust for your weight and paddling preferences. If the design weight for the paddler is 175 pounds, lets say, you may want to make the boat longer (and you can calculate fairly closely how much longer) to support your personal weight and gear.

: Sorry for the run-on here but I have had this on my mind for a while and
: every time I want to mention it, it slips away somewhere deep within and I
: lose my train of thought.

Now I am the last person to mind a longwinded posting on this board. Just pass the cookies, and umm, you got anything cold to drink?

: I'm ready to build one damn-fine, gorgeous boat and need a
: tad more direction.

Let me shout out some motivation: GET OFF THE PORCH AND INTO THE SHOP.

PGJ