, SLIME, and SEARUNNER
CENTERBOARD'S UPS & DOWNS:
Ross, I may have some answers for you, but this is so important to the Searunner
crowd, I thought I would tackle it in a broad general way.
Searunner centerboards, along with their huge skeg rudders, make our craft what they are... "The best of the ol woodie but goodies". They can also be a complicated pain in the ass.
Knowing this to be the case, we set out to prevent this from the get go, and most of it worked as planned, while other ideas did not.
LOTS OF PROTECTIVE GLASS:
After lightly glassing & sanding
"to perfectly flat" inside the trunk, and the Delrin through hull
fittings for the 5/8" silicon bronze axle pin were caulked in, I made a large 5" wide epoxy
fillet around the through hull's mushroom heads. This made the 1' circle around the through hull
a gradual 3/8" hump in the middle of the trunk. THEN we glassed everywhere in the trunk, including over this hump, with two layers of 10 oz fabric
, and applied 4 epoxy
topcoats. The through hulls were now buried under an epoxy ramp
& glass, so we cut out their centers to accept the pins later.
Next we glassed the ends similarly, over the previously applied fillets.
At the bottom, where it exits the minikeel, we made large 3/4" radii, and glassed these all around, with 6 to 8 layers of bias cut glass tapes. All of the minikeel is about 3/16" thick, except the bottom & nose, which is more.
So... the trunk was WELL glassed & tough! Since we pull the CB out of the boat from above, this extra glass at the bottom of the trunk, and subsequent narrowing of the slot, was OK.
I HATE "CLUNKERS:"
On the 34, some things may vary from the others, but... We have a split hose at the top, for a "0" tolerance but cushioned fit. At the bottom trunk's slot, I applied more and more glass to the 1' long bearing area, at the radius (forward end), just at the point that where board is fully down. I added glass until it is almost "0" tolerance at the bottom slot.
When the board is up, there is almost a finger's width on each side, but when down for sailing, the bottom tip of the board can only swing side to side about 1/16" or so. It doesn't "clunk" in a seaway, even dead down wind
. I also glued into the CB, a 4" long section of thick rubber hose, into the already HEAVILY glassed axle pin hole. This is for further cushioning & sound proofing.
WHAT IF I GO "BUMP"?
I wanted to hedge my bets in future groundings, so glassed the hell out of the board. The glass is about 1/8" thick everywhere on the sides, going to 1/4" thick on the bottom, 3/8" thick on the leading edge, and right on the small "strike zone" area where the bottom meats the nose, it is almost 1/2" thick! That takes a LOT of those bias cut glass tapes, and a LOT of fairing it out.
We have touched bottom a number of times taking out a chip, and a crab pot line's barnacles
dug 1/16" groves along the sides once, but it never got to the wood, or even close. This allowed me to wait years if necessary, before effecting a repair. Because we attach a 1/8th" parachute chord to the CBs down line, and cam cleat only the chord, it acts as a fuse. If we hit something, the chord breaks, and the board kicks itself up with a gentile thump. (This is due to the short section of 3" rubber exhaust
hose attached onto the top of the CB trunk's fwd end wall).
My approach was not to use a more water
material, like Roy has done on his new CB. I went with the much harder wood core
as drawn, but with SO much glass in impact areas, that it stays encapsulated. I applied the same reasoning to the rudder/skeg as well. I think either approach is valid.
My board is of coarse way heavier, but is still so buoyant that it is hard to crank down. Very little of this is friction, as once it comes up a bit, it is a loose fit. There IS the additional friction of the slot's rubber flap, however.
Roy's idea is much lighter of coarse, I just hope it is not too hard for him to crank down. I think that the 40's CB is controlled differently, and perhaps has better mechanical advantage than mine, so should still be manageable. On the 34, the approximately 2' of control rope
pull, goes from full up to full down, so it is actually at a mechanical DIS-advantage.
THOSE DAMNED TURNING BLOCKS:
After over 17 years of sailing Delphys hard, and blowing up 4 of the CB down line turning blocks, (1,700# WL Ronstans), I finally got fed up. I switched these control blocks out for SS Harken
ESP foot blocks, #6076. These are 2,500# WL, & 5,000# BL, with a 3/8" axle bolt! It has been several years, and they hold up to salt water
well. We also raised this down line block in the trunk by 2", so that it can be reached from above. This resulted in a bit less board down, like 5%, but the boat balances better. This is a good preemptive replacement, btw, for anyone heading on a world cruise
THE RUBBER FLAP:
This did and didn't work. I don't know how many Searunners have this feature, but it was drawn on the 34's plans. I made & installed several types of rubber flaps in my boatyard before launching, and settled on some RUGGED 1/4" thick reinforced conveyor belt material.
It was originally full length, and worked great when I pushed the board up from inside my grave sized "board pit" in the boat building. Then, a year and a half after launching Delphys as a bare hull, we stood the new mast
. I now had a mast winch
that would allow me to crank the board down for the first time since launching. On about the 10th try, the back half of the flap inverted when raising the board, and it jammed SOLID! Two full days and two SCUBA tanks
later, I had "hand sawed" off the offending part, and freed the CB. WHEW!
The problem with the flap idea is that at the slot, the front half of the CB is going mostly fore n aft, while the back half of the board is going mostly up n down. The back half of the flap could, therefore, jamb, If fact it wants to.
I split the difference and cut a wide slot in the back half of the rubber flap, while keeping the front half.
Finally something that touches on Ross's question... In year one, while we had the full rubber flap intact, even though we had only "Copper Crapsky" coating the trunk & board, (which does NOT work), we never had ANY growth in the trunk or on the board. NONE!
Seal off the light and their food
supply, and the buggers will not go there. Ross, I obviously would not recommend a full length rubber flap, but a half way flap, with a wide slot in the aft half like we have, goes a LONG way toward preventing all growth. This is especially true on the forward end, where the board to trunk's tolerances are so close.
After calling all the SR 34 folks I could, I found that they had all omitted the rubber flap, or cut it out later for similar reasons. Our new version, fairs in the front of the board nicely, partially seals
the trunk when it's raised, and works great!
ANOTHER CHANGE AT THE BIG 8 YEAR REFIT
I had started out with a wormshoe of solid 1/8" thick copper plate. It was tough, did it's job as a wormshoe, held on the rubber flap, and made an incredible lightning
As an ABYC member
I started out with a ships "common -" on EVERYTHING, like they call for, but the stray current
was like dough nuts for sea critters. Then with help from Stan Honey, we figured it out. I had created a battery! Now we isolate the DC from the lightning
ground, and this helped immensely.
The thing was, even with the mast's lightning ground isolated, the copper plate was so large, it still interacted with underwater zincs, and ATTRACTED barnacles! It ate zincs too.
During this big re-fit, I made a 1' X 8' X 3/8" thick epoxy glassed plank. Out of this I cut my current
FRP wormshoe. Now I have something STOUT for Delphys to sit on, it holds the rubber flap on, and the new smaller "isolated" lightning ground causes no barnacle problems at all. Zinc consumption
is now normal too.
PROBLEMS ALMOST SOLVED
Right? Well not yet. At this 8 year point I also started bottom painting up in the CB trunk about 18", and the centerboard
. It IS more complicated to arrange hanging in the slings over night to accomplish this, and THIS long duration cuts into your amas' bottom paint
SO... I may switch to painting the board every other haul.
On the 34, we were getting a lot of water
sloshing around in the cockpit's sub floor storage
area, which was coming from the open CB trunk at the top. We already had 4 huge scupper holes with wave deflectors to evacuate water this area, so we completely capped the trunk, but in an easily removable manner. We did put washers in between the top level cap and trunk to drain rain or our shower
This not only solved
the sloshing problem, but further reduces the light available.in the trunk, which means growth.
During the sailing season, I jump in and wipe down the hull with a soft gloved hand, the day before going out. There is usually only light slime in there, or on the board, never barnacles. Even before we started bottom painting in there after out 8th year, the growth problem was mostly solved with the combination of the halfway closed up CB slot, (due to the rubber flap), AND the top trunk slots now being capped.
CUT OFF THE FOOD
SUPPLY & THE LIGHT:
This combination, Ross, may do the trick for you. It did for us. If you also bottom paint
the board & up into the trunk with several coats of ablative, all the better! Regular "light pressure" wipedowns in the water, get the barnacles before they really attach, when they're like a grain of sand. It's easy if it is done more often.
Hope this helps,