Unconventional fin placement

[stoneaxe]

Luc...I don't think there is any question it would make the Jav more stable to have a ventral installed. The Speedboard is a flatwater thouroughbred. In order to get the tail to release you have to stand forward of the handle. It's much narrower there and for me the board becomes very unstable. Anything other than glass and I'm in the water a lot. Add the ventral and I can paddle it in chop. It doesn't respond as well to the paddle so you have to anticipate turns and currents effect it more but its a great way to tame a otherwise unstable board. If you don't like it just plug it up.

[Luc Benac]

How far forward did they move the fin on the javelin?

DJ mentioned just in front of the existing box.

[Luc Benac]

Luc...I don't think there is any question it would make the Jav more stable to have a ventral installed. The Speedboard is a flatwater thouroughbred. In order to get the tail to release you have to stand forward of the handle. It's much narrower there and for me the board becomes very unstable. Anything other than glass and I'm in the water a lot. Add the ventral and I can paddle it in chop. It doesn't respond as well to the paddle so you have to anticipate turns and currents effect it more but its a great way to tame a otherwise unstable board. If you don't like it just plug it up.

I am thinking on moving the fin box just ahead of its actual position and test this.
Then maybe consider the ventral fin - I need to get hold of Larry - I left a message on its Facebook page but will see if he gets back to me.

Cheers,

Luc

[blackeye]

It does make me want to look for one of those long US boxes that were avalibe years ago for windsurf mast tracks to put in my new board, could put it so the back of the box was in the conventional position but allow you to move it a few inches forward to experiment with.

This is a really interesting idea. One long fin box, or multiple fin boxes the length of the board. Multiple fins in various positions could be tried.

Time for some pedantry.

The balance point (Centre of Gravity, COG) of an unloaded displacement board is almost irrelevant as the rider's weight is far greater and can be moved relative to the Centre of Buoyancy (COB) to trim the board nose down or tail down. Of course, the COG and the COB have to be in perfect balance or something happens until the balance is established.

The Centre of Lateral Resistance (CLR) is what we are talking about in this thread. That is the point of resistance to sideways motion. It is made up of the resistance of the fin to sideways force as well as the profile of the submersed board. On a displacement board, it is WAY out of balance and insufficient for the sideways force of the wind. The fin on a displacement board is at the stern because its major function is to counter the rotational force of the off-centre paddle stroke, much like the tail rotor of a helicopter.

We can experiment with changing CLR by changing COG. Stand much further forward on the board to have more of the front of the hull in the water. This brings the CLR much further forward and balances the board against sideways force. Another trick is to cant or roll the board towards the wind more often than the opposite side. This places a lot of the belly of the board in the water and dramatically moves the CLR forward. This is the same as moving a fin forward or putting in a new forward fin.

A surfing or planing board also moves the CoLR but from the front sections of the board being out of the water. The board is effectively shortened and the fin, relative to the part of the board in the water, appears to have moved forward.

Daggerboards and fin keels in sailboats are there for this purpose. They aren't there for turning, but by raising and lowering a daggerboard and changing the CLR, the boat can be steered. The early 80's sailboards had those awesome adjustable daggerboards. The higher speeds of the planing boards provided ample CLR with just the tail fin and the rider's weight moved aft to be in balance.

I want a ventral fin for my SB Touring. It is a bear in a cross wind. A steerable canard would be interesting. And a DSS for lift and a swing keel for roll prevention. Something like Wild Oats XI ...

[Eagle]

If your SB Touring has a little hole with a metal sleeve in front of the fin box you may be able to purchase an aftermarket rudder system -

http://star-board-sup.com/2015/faq/

"On the 14', 12'6", 11'6" Touring, toward the stern, why is there a hole with a metal lining going all the way through the board?

The aluminum insert in front of your Touring 14′ Fin box is there to fit an after market course adjuster (steering system). It basically fits a Directional Fin on a small shaft going through the insert and fitted to a light fiberglass rudder. This can be locked at any angle in order to adjust natural course if you are paddling side wind, allowing you to still paddle from both sides even if the wind is on one side. See Starboard Touring course adjustor and more FEATURES here ."

The Expedition that never made it to prime time had a ventral type fin called "course adjuster" - also sold as an after market item -

[blackeye]

My Touring is a few years old - maybe a 2011. It doesn't have that insert for a steering system. I can't help but think that using a rudder in place of balanced lateral resistance is just slow.

In the flesh I saw a racy Starboard with tiny Pectoral fins. I should have paid more attention at the time. There are a few odd boards around Vancouver with Starboard livery.

By moving the tail fin quite forward we will have to start calling it an anal fin. (Various clever second sentences composed, then erased.)

Another reason to move fins from the very back of lengthy boards or boats is that in steep chop, the stern and fin often comes out of the water.

[blackeye]

The fin on a displacement board is at the stern because its major function is to counter the rotational force of the off-centre paddle stroke, much like the tail rotor of a helicopter.

A truer example would be the tail fin of an airplane in that it's function is to prevent yaw, exactly the same as a paddleboard.

A surfing or planing board also moves the CoLR but from the front sections of the board being out of the water. The board is effectively shortened and the fin, relative to the part of the board in the water, appears to have moved forward.

You can tell I don't surf boards. The above works for planing sailboats like windsurfers or big boats surfing straight down a wave. By digging in a rail you move the CLR way forward on a board whether it be a surf shape or displacement board.

A good sleep does wonders. Admin - I need a 5 day edit window.

[SUPflorida]

Anyone know a place in the US that sells the 15" fin box/mast track? I can only find one seller and he seems to be in France...and it's a whit , not black box...rumor for decades is the white is not as strong as the black....

[blueplanetsurf]

Anyone know a place in the US that sells the 15" fin box/mast track? I can only find one seller and he seems to be in France...and it's a whit , not black box...rumor for decades is the white is not as strong as the black....

The Chinook boxes are great:
http://www.chinooksailing.com/products/index.php?cPath=64&sort=5a&page=1

[Luc Benac]

SO I had my local repair shop put another fin box about 15" from the back.
I just picked-up the board and awaiting this week-end to try this out.

[SUPflorida]

Interested to see how it goes...looks like your boards original fin placement is farther back than the norm...hope that the sweet spot is not somewhere between the old box and new one....that would be a bummer. Lets put some positive vibe out there that it's spot on! I will be looking for a favorable report this weekend.

[Luc Benac]

Interested to see how it goes...looks like your boards original fin placement is farther back than the norm...hope that the sweet spot is not somewhere between the old box and new one....that would be a bummer. Lets put some positive vibe out there that it's spot on! I will be looking for a favorable report this weekend.

Yes I am crossing fingers. I had to decide between moving the fin box to somewhere in between or add a fin box.
Of course a fin box 25" long would have been the solution :-)

[DavidJohn]

Looks great and you should notice a difference..

Anyone else concidering doing this could do it differently.. You could router/cut a long narrow block (section) out the width of the fin box and double the length of the fin box (extending forward the length of the box).. and once removed from the board just spin it around so the original box is now forward and the blank section is behind it.. Glue it in place and glass over it.. Router out the slot and with some paint should end up looking original without the odd look of two boxes.

[Luc Benac]

Looks great and you should notice a difference..

Anyone else concidering doing this could do it differently.. You could router/cut a long narrow block (section) out the width of the fin box and double the length of the fin box (extending forward the length of the box).. and once removed from the board just spin it around so the original box is now forward and the blank section is behind it.. Glue it in place and glass over it.. Router out the slot and with some paint should end up looking original without the odd look of two boxes.

Hello DJ,
I had mention that to our repair man and for some reasons he was not supportive of this or could not do it so a new fin box was in the cards regardless.
I have zero knowledge so difficult for me to argue.
If I am happy with the position of the new fin box, off-season I will ask him to simply remove the old one or glass over it so the board looks better.
Cheers,

Luc

[blackeye]

Hey Luc, who did the install? I want to get some work done and the only shops I know won't do it.