SurfMat: Fin Mods?


I remember a while ago there was a post on cutting down fins or modifing them for comfort while riding a mat? I can’t seem to find it? Does anyone have the method?



PS… I finally have a mat now, its no Neumatic but its much better then a lilo or camping bed.

one of these…

it looks better in real life

I first bought a ‘palmbeach’ surfmat with its own self inflating system but it was crap and I took it back on got this which is stacks better and came with resin/glue a spare valve and some patches.

It rides really well and I’ve ridden it in long pointbreaks were it flies and also fun in tiny crappy closeouts close to shore.

I’m still just learning how to surf a mat but I’m getting some good long rides. I like the feeling of sticking your head over the front and trimming fastly with no board in front of you.



Josh -

Yeah, I tried to get one of those but the guy doesn’t ship to US. :frowning:

I’m not sure if this will work without signing in… George Greenough cut his down and a lot of people thought it was a good idea. Dale Solomonson set up this users group with a primary focus on mat riding and related issues… UDT cutdowns, etc.

If the link doesn’t take you directly to photos, you might have to register and sign in. It’s on

page 4 of pictures. (“Greenough UDT mods”)

Thanks heaps John!!

I really like the modification on these!!!..

New Voit UDT swim fins with personal modifications by run

George has made a number of other subtle changes since these photos were taken. Note: the fin blades’ bottom taper is “cupped”, the heel straps have been re-shaped to an asymmetrical fit for inside/outside (higher-lower) ankle joints, the interior of the foot pockets have been re-shaped and lined with thin sections of neoprene. George’s modified UDTs are quick, comfortable and powerful.

Most swim fin users with normal size feet do not need such extensive UDT modifications, especially if they weigh over 175 lbs.

I find a hacksaw pretty useful in cutting down fins, they’re straight and have small teeth.

looking forward to shaping another pair

and inserting neophrene too


a non giant but serrated steak knife sprayed liberally with silicon or wd40 seems to work good for messing around with the outline, 80 grit on a disc sander seems ok for the refoiling duties

million ways to skin a cat of course good luck and have fun

Has anybody here tried Da Fin swim fins? I recently bought a pair in Hawaii last year and had a chance to compare them to Ambrose’ greenough modded UDT’s. They seemed to have about the same surface area in the blades. I didn’t get to use them though and was wondering if any one has comments about the performance differences.

I want to get another pair of fins I can wear without booties and would like to know which would be a better choice. Thanks.

da fins look sweet …i know mark cunningham and keith mallow both use them…have a short edgeblade like vipers but shorter that hold you against a wave…havnt used em yet but i definitly want a pair…they come in 14-16" foot pocket so you can use booties with them…ducks or udts without modification wont work for someone with size 14 feet(me)…im just waiting for da fin to put out 14-16" in the northshore model…(the red ones with stiffer rubber=more power)…theyre really as big udts???..doesnt look like it…7" vipers yellow dot(stiff) have the same length and width as duck feet but lack in power due to their flimsyness…they do have a more comfortable pocket then the ducks though…i plan on buying a new pair of vipers (for bodysurfing/bodyboarding) and laminating them with carbonfiber to overcome the flimsyness increasing power…i modified my ducks by grinding the center rib all the way down (on both sides) and slitting the top of the foot pocket 2/5ths of the way down and drilling holes in the top on each side of the slit(towards the edge)…after vulcanizing the rubber with a open flame(to keep the slit and holes from tearing further) i strung shoe laces through the holes and and ended up with lace-up ducks…they are so much more comfortable and have a quicker acceleration time by removing the rib…greenough grinded all of the ribs down flat and carbon fibers them(or he did)…he calls them “blanks”…greg deets id putting out softer ruber duck feet and udts in churchill green and natural gum…heres a drawing of the layout…old skool

Is this what you were looking for josh?

since this posting i have thinned the blades more and cleaned them up a lot. those first pictures are very crude. i would have posted more pics but my camera got stolen by a hotel maid. oh well

I have a pair of Bob Davis (Finman) Wave Blades that I use occasionally. The requirements may be different from mat riding, but I’ve experimented with a number of fins, including Vipers, and I keep coming back to the tried and true Churchills. The main difficulty with Vipers and come of the others was in keeping them on my feet. I seem to need the elastic behind my heels, the non-stretch straps don’t work for me. I do have pretty weird feet… I would like to cut the Churchills down to make wading easier, but I wasn’t sure what size/shape I should end up with. I’ll browse that thread for some insight.


Aren’t the blue-marbelled UDTs (UDeeT) much more flexible than the original black UDTs? How much more flexible will the brown/green UDTs be? Considerable.

isn’t the main reason UDT were so popular was because they were stiffer and more powerful? Why would you want even more flex?

I’m waiting for new UDT stock, and had planned on going with the blue-marbelled ones - (red marbelled any more/less flexible?) - just wondering now about the green/brown more flex ones soon coming out.

when i talked to deets about the pair i purchased, he said the only difference was the color itself. but i didn’t ask about the differences between the old ones and what he is making now. also hadn’t heard he was making brown and green, very cool.

the stock udt was twice as powerful as anything else i’ve tried (tech fins, churchill, bluntcuts…) i just cut them down to reduce weight a little, make them snappier, quicker, and also easier to walk on rocks,etc.

yea - that length makes em a bear to walk with. wuz surfing a point last week, where you surf down and walk back up to the point to jump in. I use blue streak duckfeet now - whutta muther gettin in, climbin, crawlin, gettin knocked over boulders. wanna get UDTs - but yep i’m thinking about that Xtra length (clumsiness)


I would like to cut the Churchills down to make wading easier, but I wasn’t sure what size/shape I should end up with

I have been using the Churchill Slashers for the past couple of few years. What got me interested in them was the lighter weight and “lower profile” compared to the regular Churchills…and an interest in the Cabell/Doyle philosophy from when they took a swim around Kauai without using fins at all, figuring the human body was evolved for swimming without 'em…something like that. Also, the Slashers travel nice in a daypack either walking and scrambling down rocks, through airports, and sneaking along on work trips. Stealth!

Fast forward a few years, since time seems to be permanently stuck on FF no matter what I do, and I find myself wanting more power for the day to day and maybe even the travel part too. I’ve seen the new UDTs and I’d gladly give them a whirl but I can’t get around the foot pockets. They just look like foot destroyers. Same with Vipers. I have fin socks I could use I suppose, but I’m into less equipment whenever possible and am always willing to compromise a bit for the sake of de-complicating life.

Having foot pockets made for left and right feet…that just seems so basic…I only have two left feet on the dance floor, right? Best fit always trumps power in my book.

As to the Churchills, I wouldn’t trim them down at all…I’d play with my wading style to become more efficient…the standard Churchill design ought to have some kind of design award for form, fit and function.

Hello Skamatt- Whoa! These time-warp threads always catch me by surprise. When I said that the dafin fins were about the same area I was referring to the greenough modded fins. The stock udt’s are much bigger. I don’t know that stiffness in fins is necessarily a good thing. I guess it depends on where you want to be on the power vs. comfort curve. I prefer to stay on the comfort side myself. It seems that the udt’s are too much for some people judging by how many are modifying their fins.

 If you order dafin be aware that, although I have a size 10 1/2 to 11 foot size, the 11 to 12 fin fits snugly on my bare feet. I also have the 15-16 size that I wear with O-neil reef booties for when I go on trips where the bottom is rock or reef. For some reason they call those the "big bu" model even though they are exactly the same fins.

i havnt heard of any differences between the marbled udts and the flat-black guesssing there will be a loss of power but maybe not as much as the modification above…the edge-blade will help trap water on the downstroke increasing thrust while the modification would be stealing both stiffness and edge at the same time while grinding…the new rubber will make the footpocket more comfortable,increase acceleration through the new-found flex of the blade and help ease putting on the fin itself because the heel strap will be made out of the same material…i have modified two pairs of churchill makapus…one for myself and one for my little brother who wanted to try Dropknee on his bodyboard…i modified mine by

cutting the trailing edge down level with the rest of the fin(blunt cuts).(DO NOT GRIND THE RIBS DOWN)…it will just further decrease thrust…i used a kitchen knife…do this outside as it gets messy…i made the mistake of doing it in the kitchen which my mother wasnt to pleased with(i was 15 at the time)…i didnt like the uneven pressure on the foot when kicking…the reason makapuus are shaped like this is for bodyboarding…it increases holding edge on the face of the wave(prevents sliding out) while not adding drag by having less fin in the water…


i didnt like the uneven pressure on the foot when kicking…the reason makapuus are shaped like this is for bodyboarding…it increases holding edge on the face of the wave(prevents sliding out) while not adding drag by having less fin in the water…


The basic Churchill design seen on the Makapuus predates bodyboarding by about 35 years. My understanding on the shape of the fins is kind of two parts: one is that if you put them on and look at them side by side you see the same basic shape as a dolphin tail with hopefully the same natural power. The other is that having the long edge on the outside it decreases pressure on the big toe area, drastically reducing the dreaded big toe cramp, which used to torment me like the freaking Hounds of the Baskerville with Duck Feet. But you are absolutely spot on with your observation of bodyboarding usefullness…maybe no small reason the Morey people picked up Churchill as a companion product.

It’s has amazed me for two or three decades now that nobody tries to sell a bodyboard and fin combo - especially Morey. Some kind of pricing/special coupon deal so the customer could get the right size…and thus locking in a new customer to the corporate product line. But then I’m just a simple man, leaving no tracks on rice paper…