I am starting my first balsa this weekend. I’ve asked and recieved great advice on the hollowing aspect. Now another one…
Is there a rule of thumb on the thickness difference between a poly foam board and a hollow balsa so you might keep a similar buoyancy?
I have a nice California gun John Mellor made for me and it is about 3 1/4 inches thick. I want to replicate the board. How thick should I make the balsa board?
Not exactly apples to apples, but I notice my hollows float about 1/2" thicker than foam…
EXAMPLE: an 7’6" x 3" foam board floats the same as a 2.5" hollow…
Go forth boldly…
Send pictures…
Paul
Paul,
If your wooden board is denser than a foam board and the same shape and volume then it will have less buoyancy than the foam board not more as your answer implies.
Lee,
As an engineer you should be able to calculate the extra volume required to maintain buoyancy when using a denser material, it’s fairly simple isn’t it ?
Scientific theories and physics be damned…!!!..
I stand by what I said…
They feel lighter in the water, and seem to float thicker…
Plant seeds and sing songs,
Paul
I recently got to ride the Quigg reproductoins I built in Hawaii, An 8’6" and a 7’10", they were both chambered and I had my worries that they would not float very well.
When I jumped into the shore break at Val’s reef, I was more than suprised at how high I was out of the water on these two boards.
Last summer at Malibu I rode a Quigg repro of the Malibu chip, unchambered, 35 lbs. it too floated amazingly well and I thought it would be a real sinker.
You look at old photos of people tandeming on the balsa/redwoods, both knee paddling, obvious floatation going on there
I have, by far, the least experience with this of the folks that have responded to this post. I’m sure it all depends on the techniques you use, but I ended up with a sinker with my HWS fish. I was so afraid of not being able to duck dive it, that I thinned out the nose to about the same contours as a modern poly shape. The result is that it duck dives really well, but, at 18lbs with low nose volume, is a b**ch to paddle and catch waves with. If I did it again, I’d err on the side of a little too much buoyancy. My 2 cents. Have fun with the project!
Pat
Answer me this:
How does Paul’s answer imply that his board is more dense than a foam board of the same shape and volume?
Roy,
It seems to me that you can sometimes be a great contributor to this forum, but your greatest flaw is your abrasive writing/typing style combined with your insatiable drive to see the error in people’s posts, to the exclusion of thinking about how another’s statements could be correct.
If you believe this to be a personal attack, I believe that your ill-advised and hasty questioning of other people’s intelligence for your own amusement is one and the same. Please, read carefully and think before you type.
JSS
In your never ending quest to say something about everything, you failed to actually read the post; “…rule of thumb…”
I don’t have the time or inclination to make a mess of my bathroom by submerging the existing board to measure the displaced water, or spend several hundred dollars having the board scanned, or spend several days using Green’s Theorum and Stoke’s Theorum to calculate triple intregals to determine the volume, or estimate the volume measuring chord lengths at infinately small intervals. Then do the same thing with the balsa blank, then estimate the volume of balsa removed during the chambering process.
The amount of error from the estimating performed in that analysis would far exceed the tolerances I was looking for.
I’d much rather waste my time responding to inane, pointless comments from Swaylock’s resident bore.
Thanks Paul, Jim and Pat. I’ll let you know how it turns out.
Oh…I almost forgot…
I’m confused if you are doing a chambered solid balsa, or strips on frame?
I’ve got one of those blanks Keith and I picked up last year so it will be a chambered solid balsa.
I’ve got one of those blanks Keith and I picked up last year so it will be a chambered solid balsa.
Cool! So Lee, what is your intent? It’s a gun, so what size and for what kind of waves? Some of the bigger guns I’ve seen in Hawaii were pretty full thickness and rode well in the windy offshores.
I wish we were closer in location as I’d love to help, or watch.
Hi Lee -
I don’t know of a specific “rule of thumb” - balsa densities and chambering techniques are different so the overall weight of the finished chambered blank would be impossible to calculate. I’ve lifted chambered Balsa boards that were actuially lighter than foam boards.
I remember your board had 3/8" Basswood offsets and double !/8" wedged stringers so it wasn’t exactly a lightweight. That “Gentleman’s California Gun” was designed to get into bigger waves easily and not designed specifically for tube riding. The thickness was intended more for paddling into waves with a possible trade-in for rail sensitivity. I also ordered that blank with increased nose rocker thinking that if you ever took off late on a big one and pearled, it would be all my fault.
I also remember adding some bulk to the rear rails on a solid balsa I made for myself thinking I might compensate for the weight. Once at speed, the overall weight of the board doesn’t seem to be much of a factor. I might have liked a thinner more sensitive rail in certain situations but at my age, thick seems to paddle better. In bigger surf, just getting into waves is my priority. How many times have I sat in the lineup on good days and watched as shortboarders just weren’t getting many sets?
IMO you could probably make your new chambered Balsa as thick as your current foam board and be alright. If you wanted more rail sensitivity, thin it out. Bulky rails are OK at paddling speed but can be harder to control once your up and running on the wave - even with a heavy board. Sorry - no rule of thumb.
I stand by what I said…
They feel lighter in the water, and seem to float thicker…
I think this is partly from the same reasons that the EPS boards are believed to float so much better…(They do float better, but it’s very marginal. half a pound less board is not going to float a 160lbs surfer that much different). Unless you make the cross sections for the hollow very crowned, you are going to end up with a board that are a bit thicker towards the rail although the rail shape may be exactly the same. Same thing for the EPS boards shaped out of the squared blanks, they end up being less crowned than a regular blank. Just plain more volume. This is all IMHO of course.
This is a picture of the board I am going to replicate. I’ve tried all manner of magic to get the picture to post but to no avail. I will be thinning the rails (mostly in the tail) and perhaps narrowing the nose a hair. The board rides great but likes really smooth conditions. I attribute that to the overall thickness. An increase in weight is just fine for what I’m trying to do.
http://www.swaylocks.com/forum/gforum.cgi?do=post_attachment;postatt_id=11824;
Answer me this:
How does Paul’s answer imply that his board is more dense than a foam board of the same shape and volume?
It doesn’t, but you will notice that i said 'if '. . . . ( if Paul’s board is denser than a foam board, and it is the same volume, it will have less buoyancy)
Any answer to this question which doesn’t take into account the likely density of Lee’s chambered balsa board compared with the foam board it is copied from will be meaningless. Of course if the thread was just an invitation for a vibefest then no correct answer is required 
I’ve got one of those blanks Keith and I picked up last year so it will be a chambered solid balsa.
I resently made a chambered balsa board. Here are a few of my lessons learned.
– Be selective and choose the lightest wood possible
– Shape you board first, and then do the chambering. You can remove much more wood without having to worry about cutting into the chamber later.
– Use draw out your chambers with a dark pen, and then use a router to cut nice clean chambers.
– Make lots of small chambers. Big chambers are not as strong.
– Stagger your chambers. This it is also stronger. You don’t want your knee to go through the chamber.
You should be able to reduce the weight of your board by more then 50% if you do your chambering well.
When designing my board I used APS 3000. I copied the outline and the bottom rocker of a foam board that I liked. I then modified the top profile to increase the volume of the board. APS 3000 is nice, because it calculates the volume for you. The original foam board had a volume of something like 32 liters. The design of my wood board ended up being about 40 liters.
If you want to get all scientific, then take two pictures of the boad that you want to replicate. One from the top and one from the side. Import these pictures into APS3000, and create a model. This model will tell you the volume of you board (bottom right corner of the screen). Next, weigh your board.
See the following link to learn about buoyancy:
http://en.wikipedia.org/wiki/Buoyancy
Figure out the weight (i.e., mass) required to sink your current board. This includes the weight of the board itself.
The wooden board that you build will have different volume and weight. Vary these two parameters so that your new board requires the same amount of force to overcome the buoyant force as does your foam board.
I know this isn’t a rule of thumb. I guess its more like a rule of fingers and thumbs.
Lee,
If you send me a picture of the side rocker and the board measurements, then I’ll import it into APS 3000 and do the volume calculation for you.
Note: I’m going out of town this weekend, so I won’t be able to get back to you until Monday.
Cheers,
Scott
Thanks, I appreciate the offer but I’ve got all the info I need now.
Quite a strange thread Lee.
First you asked for a ‘rule of thumb’ in order to estimate the difference in buoyancy between a chambered balsa board and an identical foam one.
The information posted in reply tells us that chambered balsa boards can be denser or less dense than their foam counterparts.
It isn’t possible, on the basis of that information, to decide whether or not volume should be added or subtracted from the balsa version, so it isn’t possible to make a rule of thumb or estimate without further information.
Nevertheless you have decided to reduce the volume of the board based on the buoyancy information given.
It beats me how you figured that one out, unless perhaps you have reason to believe that your finished balsa board will be lighter than the foam one.
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