Hi guys, I just glassed my first fin. I used 3 runs of the rovings cord And 2 layers of cloth, it feels strong but looks pretty thin. Its a 10.5" Single fin. A guy on a facebook page said that I should have done 8 on esch side, and that I should add a few more to make it stronger. The question is, Should I just add then over the existing and then add another layer of cloth, or do I need to start the whole process again? Thanks a lot.
Guy on Facebook gets a thumbs down from me.
The roving is there to help with a transition from board to fin, not to provide strength.
Less is more when it comes to roving. - if you can get a tight (air bubble free) corner with just glass - no roving, even better.
The bigger the transition (filet) is the slower that fin is gonna be too.
Others may disagree, I’m ok with that.
If you run your glass layers at opposing 45s that will help with strength aswell.
Thanks a lot!! It feels pretty strong! Might leave it like that! If I loose the find, will came back to you! Haha thanks!!
Yeah, and if you do such a wicked hard bottom turn that you blow out the glass on one side (or the more likely event of whacking it on something between your house and the beach) the glass on the other side should prevent you from losing the whole fin. Just clean it up and re-install. Not a big deal.
You may think that roving adds no strength, but you are wrong. If it were purely cosmetic; Why not use Cabosil ?? The norm is; Three strands per side of eah fin. Glass cloth ; Three layers of four ounce per side. Two six will work, but obviously is weaker. Just do the math. This recommendation is for Thruster fins. In your own judgement you may want to go a layer or two more on a single fin, do so. What you have done there looks good to me. Fat bases and beads are old school and less efficient. More about looks than performance. Repairs are a differant ball of wax and my recommendations for that would be differant. The more glass and roving you use; the bigger mess you have to repair when it snaps. Eight layers per side is ridiculous and would result in the kind of mess I just spoke of when it snaps. I have yet to see anybody glass on a fin without some roving and not have air bubbles in the glass. Not to mention how week it would be at the base. An easy snap.
Well stated. The strongest glass-on method, for fins, is glass only @ 45/45 bias. I adopted that method in 1960. After that, I never had a lost board to the beach, result in a cracked or broken fin.
Hi McDing, I have glassed quite a few fins in without rovings. You have to be careful to keep air bubbles out of the corner but it’s actually not that hard. I’ve never had any issues with the fins breaking out. I dunno man, I reckon rovings are really just there to make a fillet to make glassing and sanding easier. Sorry to disagree with you but I don’t think they add much in the way of strength.
hi, i am with Bill on this one , cloth on the bias 45/45 all the way , the beauty of cloth this way for the fillet is you can stretch the first few layers thinner , cut them 3/4 inch wide and then pull on the ends and they will pull down to 1/4 3/16 or so to taper the filet nicely ,
when a fin breaks at the base using strands ,the strands go length ways and the sideways force to break the fin just separates the strands where there is no strength in this direction just resin and the outer layers of cloth,
if i am going to spend time glassing fins on ( think bonzers ) i only want to do it once and do the best job i can so for me its all cloth on the bias and no strands , pete
Hi Pete, I can’t seem to make any sense out of what you just posted. I get the feeling that there is some helpful information there. Any chance of a bit of a re-write? Cheers. Dave.
If you try breaking off a glassed-on fin with a hammer or your hands, you will see that most the strength is in the lamination between the fin and the board’s bottom. The bigger the area, the stronger the bond and the stronger your fin attachment will be. I’m sure there is a point where the lamination strength is more than the tensile strength of the glass and you can break the fin without delamination but I’ve never encountered it, but then I’ve never used glass less than 4 oz/yd.
Never stick a fin in a slot cut through the glass and into the foam prior to laminating. When the inevitable bump happens, the fix will be a nightmare.
Just has been my experience that the roving does add strength. In the 70’s 80’s and even the 90’s(especially in Hawaii) there have always been a fair amount of glass ons. Having done lots of fin repair over the years it has always been my experience that fins with a fair amount of roving were less likely to snap. I always chose a lesser amount over the “old school” heavy build up. A heavy build up of roving when snapped on reef rocks wants to take the whole tail with it. If I we’re doing a new board with glass ons I would do it as I described. I don’t want anybody coming back to me crying that their fin fell off. You do it your way. I’ll do it mine.
…McDing is right, also Bill, Wideawake, Pete and LeeV.
I make fins and glass on those in weekly basis for around 30 years now; there are also a % that I use 4WFS and fusion boxes.
So yes in the beginning like many shapers, I tried with too much roving strands, without the strands, with aerosil, with resin without charge and some made lots of boards in the early 80s with epoxy instead of strands I even saw guys using silicone…
You saw plenty of stuff in the past due to not have the right materials; boards to show and not to use in the surf; pop outs; low quality series; etc were other times now we (also the rookies) have this type of forum that you/us can discuss design and techniques and many see stuff that seems apparent but in the past took many moons to achieve that knowledge or to have the right method depending on the surf conditions (Hawaii; small pumping surf; hot dogging surf; tube riding)
-In my opinion, how many layers depends on those conditions and the type and size of the fin/s.
-4oz is the way to go in most situations but on some fins is better to mix a heavier glass to prevent tiny bubbles.
-With big fins is better that the first 3 layers cover all or almost all the fin shape; then you can add smaller and staggered patches at 45º.
I think that facebook guy could have said 8 strands not 8 glass layers.
hi, Dave ,sorry if i did/nt make myself clear , just get a piece of 4 oz cloth and cut a piece out of it at 45 degrees or so ,say an inch wide and about 6 inch in length,
then pull gently at either end and you will see what i mean ,
i just use this method to build up a tapered fillet, pete
Ah yes, now I see. I’ll give it a try. Cheers.
Wow, like reading posts from some parallel universe.
- 26 strands from 24oz roving.
- 2 layers each side of football shaped 6oz. No advantage doing the whole fin and a problem if it’s a flex fin, a shell doesn’t flex.
- a big fillet is stronger with a bigger footprint and the bigger base reduces drag gives better edge control. In my opinion the fillet on a glass-on is the main advantage over the lack of one with a box fin.
https://en.m.wikipedia.org/wiki/Aircraft_fairing
Glassed and ridden several hundred boards with glassed on fins using the tried and true method of fin rovings at the base covered with a couple or more layers of cloth. Broken a few fins off, but it wasn’t due to defect in glass, more like close encounters with rocks or an ankle. I’ve never done Thraillkill’s method, but sure seems like it would be plenty strong.
Is a fin box system more efficient for water flow? Maybe, but some of my favorite (and fastest) boards ever had glass ons with the fillet. That said, some of my favorite boards have been boards with fin boxes/plugs. I don’t know how to quantify which is better other than taking a board with glass ons and grinding the fins off and reinstalling with plugs/boxes. I’ve done this, and honestly, the board worked the same for me. Similar projection/looseness that I liked about the board prior to modification.
Your results may vary…
Use to use 8 roving for thrusters up to 16 for singles on big long boards…its not the rovings giving strenght …more the radius fillet created …roving has a grain that will crack without the layers of glass oustide. Living and surfing in bali indoesia …fixed fins verse removable fins what every works .currently riding generic black plastic fcs dont mind the flex. You adapt Go surfing dont stress .meant to be relaxing…
I agree with Gene. The bigger foot print at the base and out onto the tail is the most important part of the process.
…I can add that regarding failure decades ago with the glass ons mainly in not so quality boards was consequence of the light glassing and the sanding man sanding through the patches; so if you go light with the patches and then you sand too much with the angular sander the fin only would hold by the fillet and a bit more.
Glass-ons are cool; but try changing fins or repositioning a fin forward or aft and you’ll know why a fin box is more functional.