Hemp balsaperimeter.

General Discussion
1

I finished my third hempboard two weeks ago and have ridden it twice in small beachbreaks.

It was built using 1pound eps, hempcloth of the finest kind,balsa for the perimeterstringers and epoxy resin(RR epoxy fast hardener).

The board is 6’ - 18 3/8 wide 2.5 inch back-11 1/16 nose-14 1/8 tail, deck is concaved a lots and thickest point is about 2 inches thick.

the rocker and foil was taken from a board I used to ride and the bottom is flat all the way.

fins were made from 9mm plywood and were glassed on.

after the blank was cut out from the eps block and shaping done, one layer of hemp was vaccumbagged on deck and bottom. And then I put on the balsa perimeterstringers which was made out of two 4mm thick balsa planks 900mm long 80mm wide.

Then another layer of hemp on each side was put on , hotcoated and sanded.

I was quite happy with the weight at 2.5 kg, my first hemp weighed almost 5 kg.

the board paddles alright but when you duck dive you can feel how soft the board is which turned out to be a bad thing…

The board doesn’t work…

When you paddle for a wave on the board everything is alright til you put your hands on the deck to stand up, suddenly it feels like your stepping on the brakepedal…it slows down and

I miss waves I know I can paddle in to. It must be that the board changes its rocker when I put the hands on the deck because its so soft.

And when youre finally up it feels dead and is only manouverable in the more steep sections.

So now I want to stiffen up the board so it becomes a ridable board. I have thought of two methods, one is to split the board in half and put in a stringer in the middle or to laminate a layer of carboncloth on the deck since I hear about carbon being stiff.

Or maybe it’s not because its too soft…

Ive attached some photos

Jimmy yoshio shibata.



2

more photos.


3

hi yoshio

too much flex eh???

i would first try a few layers of four ounce on the rails

that would stiffen it up heaps im sure

4

thank you heaps for the photos and the honest appraisal , Yoshio …

your report confirms a few thoughts and questions I had previously, regarding this whole “eps blank” bizzo .

…thanks for answering !

I hope a layer of carbon fibre top and bottom will stiffen and strengthen up the esky foam .

Let us know how you go , eh ? [I hope <span style=“font-style:italic”>that</span> option works , rather than having to cut [?gut?] an already glassed board , and re-stringer it . [That sounds a pain , to me]

If possible , I’d also really like to see and hear about your two previous hemp boards , please ? [if I’ve missed them here previously , then … just the links to those threads would be good…]

cheers !

ben

5

shock horror …

id swear i was looking at one of my boards …

yep yoshio , youve got to much flex , one other consequence of that will be a late drop , as your weight gets pushed into the board with extra g force , itll bend and stall just like youve already experienced …

all is not lost …

all you have to do is stiffen up the area either side of your front foot …

if you stiffened it for 3 feet or 45 cms either side of your front foot , i think you could turn it into magic …

it would be a real eye opener to the importance of the right flex …

as a general rule , the stiffer the construction technique , the thinner the shape to get some flex back …

this is my recomendation …

get 3 or 4 pieces of 3mm 100 x 900 balsa , and vacuum a panel down ,right where your front foot goes , sand the deck a lick of resin …

something like this , blend the edges , maybe round the corners a bit , or give the front the look like it follows the outline , one layer of 4oz over that …

you will create a stiff panel that will carry your weight over that area …

i think you will freak at the difference …

ive made exactly the same feeling boards in the past …

i know exactly what your feeling …

hey nice outline …

regards

BERT

6

drats, cant see photos for some reason

i wish i could build one thats too flexi

my first board, a mal is still the best to date

7

nice work there jimmy…

my second composite had a soft spot about 18 below the nose tip…it buckled there on day two…

i needed to fix the board quick so i routed a 6mm wide 15mm deep slot about half meter long on the deck…i shoved a balsa stick inside with some foaming pu glue (Gorilla) like a partial depth stringer…sanded it flush then covered it with 2oz glass along its length…worked great to stiffen that whole section which was very soft along the crease…just an alternative

8

hi Jimmy,

Nice board. Its nice to the Dr. in the house to make things right. thanks for posting your observations. This will help me determine how I go about my first board made from EPS and RR epoxy.

I think it emphasizes that the materials you use dictate how thin you can go and if you can concave deck.

Using Berts shapes, thickness, and foils without the skins apparently does not work. I would be curious if you did not concave the deck if the results would have been better. I plan on trying to duplicate his planshape and rocker on his ‘favorite board’ with a pvc middle stringer. I was also considering putting concave on the deck, but now I am not so sure.

Thanks again Jimmy for the heads up

christian

9

i think this highlights one of the current downsides to this area …

even tho the scope of possibilities is endless and the magic you can create performance wise is uncomparable …

thats where doing the time , brings the experience …

my personal feelings is yoshi knew it would be flexy , so he was looking for the boundries …

buying a urethane blank and glassing it is a tried and true formula , theyve had 40 years to figure it out …

but the best you can get is still only 7 compared to 10 on the scale of results in composite …

my very first ones , were right on the mark , very similar to todays ones …

then a few years of doing duds till i got a feel for it …

if i hadnt of made a few magic ones early , i may not have realised the potential …

but there is the whole balancing act …

just like shape , its give and take to compensate for different variables you throw in …

same in composite combos ,add something stiff , do something to compensate if its to stiff or to stiff in one area …

thats where with this type of construction you have a lot of control over the finished result , but sometimes you can lose control equally as bad …

but like cj alluded to , i think yoshio just saved alot of other people some pain …

regards

BERT

10

This is exactly what we need … things to not work out. When we were all have successes I had the feeling that we weren’t truely making progress. Its especially helful when Bert bring up way to fix the difficulties we encounter (from this I learned the importance of panel strength in relationship to flexy rails). I fully expect my next couple board to be stunning flops. Now that I know that it is possible to retrostrengthen the board I might push the boundry a little further.

11

cool board yoshio…so of course my questions would be why was it too flexy??? to thin? balsa to light? is hemp cloth flexyer then glass? intresting to have duds… i have been finding that my boards work when the waves are pumping but suck ass when i have to pump them for speed in weak surf…

today i started on 3 boards that will all be the same outline, rocker, fin setup. pretty simple/standard short boad numbers…6’4" 11"N 19"W 14"T. I am going to vary the thickness and glass… they are for me, my girlfriend and a good buddy so we can all switch them around and see what there is to see…

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12

yoshio, the board looks certainly very good and nobody can see that it surfs like a matress. while sailboarding, we experimented a lot with flex and the best lessons we learned from the flops. to stiffen them up and get them going we used carbon fibre band about 2 inches wide and laminated those on the deck. first one in the center and if it was not enough, one left and right ( a bit shorter so you do not create a break line). this is easily done and will change the character of the board as well as create a wealth of information for your future design work. in case stiffer is better you can continue on the bottom, first one in the center and so on. the carbon band is very thin and will not require a hotcoat on the deck (but on the bottom), so its easily done.

in sailboarding we learned that a stiff center line (call it stringerline) was essential to keep up speed and momentum and that a flexible railline had very positive effects. but surfing could be a totally different ballgame, who knows…

13

on a sailboard the power comes from a different place to the surfboard …

transfer of energy is essential …

sailboard is all through the sail ,transfered through the mast down to the deck box (mast base) , and then through the board …

transfer of energy is still essential with a board , the load has to transfer out from out feet though , through the board to the water …

we also can take advantage of free energy , from the drop and any hard rail turn we do at speed …

thats where the rail line becomes important coz that is the part of the board getting the most load or force applied when we bank into a turn …

so just like drawing your bow to shoot an arrow , we can load our rail and shoot out of turns …

so in a board there are key areas where the load has to transfer from the rider through the board and from parts of the board back to the rider …

on a surfboard we rely on more of the rail line …

but on a sailboard the front half of the board near the rails doesnt do as much at speed under load …more is happening in the tail half , and centre , both energy from sail to board and from boom through rider to board in tail area …

i will throw another point in which backs mikis comment , but adds a bit more …

i did a bit of sailboarding when i was younger , but mainly where i picked up most information was making sailboards , i ended up making them because i was doing sandwich construction , so i always got roped into sailboards …

it was important to keep the centre stiff like miki said , with a firm mast attachment , and the deck and rails under the rider , but the nose and front half rails could have way more flex , to help cushion the ride from the bumps experienced at those speeds …

the bulk of the power came through the mast and rider and had to transfer to the water via the tail rails and bottom , but the nose acted as a shock absorber …

but in a surfboard we still need our front rail for loading and unloading , we actually use the whole rail line when surfing hard …so its important that our rails arent to floppy , in comparison the the rest of the board …

regards

BERT

14

Thanks for the tip on the carbon and how to systematically stiffen and modify the board. Your centerline strip of carbon sounds a lot like Bert’s horizontal stringer.

jlp, I will be very interested in what you find out in the three board test. Keep us posted!

15

Yes bert it was shock horror, but it got me thinking of many things so now I know better.

I think I’ll go with the balsapanel this time but the carbonfibre method sounds interesting too, I mean that only 2" strips will stiffen things up.

jjp, everyting I used to build the board with was flexible, the core, the cloth and the balsa too. Hemp is (from my experiences) much flexier than glass.

Smart to build three boards with same outline, rocker but change the thickness…something I would like to try.

Thanks everybody for suggesting different methods.

Will post after I’ve stiffen up the board but that will be later cause now I’m working on my first ever longboard ( balsa sandwich)for a friend and I dont even longboard!!

Good to have good friends who let you do things…

Jimmy yoshio shibata.