20+ Footer - Building in Hawaii

[Jim Donovan]

Hi Jim, doubt you need a confidence booster but I have done virtually the same thing, and the original SKUDs also. 2 x M10 CSK MT up from underneath and being able to pull the fin out is really nice. We plan on trailering the boat with the fin out. jB

Thanks JB - The GP 26 Bulb has 3 x 16mm pins that go horizontally through the fin which is set in a very deep recess; super secure but good luck trying to remove the bulb! It's a 70% heavier bulb than the 20's, so wanted to make sure this was never a warranty issue.

 

[Jim Donovan]

Been in the fridge/shed through the holidays and making progress.
Cast the recess plug into the top of the bulb and was super happy with the outcome.
Used resin/milled fiber mix and must have lucked out with getting the consistency just right.
When I pulled the plug out of the bulb, the recess was "perfect"; no repairs needed

My "lifting thing" has been ideal as it's perfectly aligned to assist in removing the recess plug.
Needed about 400 lbs of vertical pull to extract it.

Also got a first pass of filler on the upper side of the bulb; the bulb was about 45 degrees F, way to cold to apply filler. Set up my oven with the hair dryer and went off to do other stuff.
By the time I got back to the bulb it was almost to hot to touch; 160 degrees F? Okay . . . so now it's too hot . . . 40ish degree shed cooled it down fairly quickly.

 

[Jim Donovan]

Set the fin into the recess to have a look; easy to get set up perfectly using the 'lifting thing" again with the laser level. It's a big fin for a 20 footer!





Fin got a final covering laminate of 200gsm (6 oz) carbon twill, and is much prettier now.
Struggling with the concept of clear- coating the fin now . . .

This laminate is primarily needed to hold the kelp cutter tube onto the fin, and get the fin up to the desired thickness.

 

[Jim Donovan]

"Final" bulb fairing process went pretty well. There were a few low spots in the casting around the recess area, where the pour spout was located.

(Know how to do that better now; my casting crucible was a bit too small to get large enough sprues to deal with the shrink-back as the lead cooled.)

Little bit of Fairing 101 next:

First pass with a DA sander was only to get the obvious lumps and shiny/hard exterior surface on the fairing removed. You need to be super careful with a disc sander to avoid introducing flats onto the surface. I use low pressure and keep it moving diagonally like you would a longboard.

After the surface is ready ONLY use a longboard using diagonal strokes in both directions. I used a 2" wide piece of foam core with a strip of 50 grit sanding belt spray glued to it.

Eventually you get a surface looking good; you want to see consistent scratches in both directions. There will be obvious low spots; they still have a shiny un-sanded look. These were located around the recess on this bulb.

First I draw around the lows, and then using a small sander, carefully scuff the shiny surface in the "dents". You NEED to scuff the shiny surface or the fairing won't stick 100%. Drawing around the spots makes sure you don't loose their location after the scuffing.

Filler gets applied carefully in the scuffed area; the surface around the dents is fair and you want to avoid sanding into that surface. Don't apply a big lump that's difficult to fair without getting into the surrounding surface - you may need to do an additional fill after. Fairing the spots will eventually revel the lines you drew; that's when you know it's time to stop sanding.


I like to to use a slightly thickened resin (cabosil and black pigment) to coat the bulb after I think it's pretty good. The cabosil keeps the resin from sagging, and if you're lucky, self levels beautifully. The black/shiny surface reveals anything that looks odd.

Looks pretty good . . .

 

[WCB]

"Final" bulb fairing process went pretty well. There were a few low spots in the casting around the recess area, where the pour spout was located.

(Know how to do that better now; my casting crucible was a bit too small to get large enough sprues to deal with the shrink-back as the lead cooled.)

Little bit of Fairing 101 next:

First pass with a DA sander was only to get the obvious lumps and shiny/hard exterior surface on the fairing removed. You need to be super careful with a disc sander to avoid introducing flats onto the surface. I use low pressure and keep it moving diagonally like you would a longboard.

After the surface is ready ONLY use a longboard using diagonal strokes in both directions. I used a 2" wide piece of foam core with a strip of 50 grit sanding belt spray glued to it.

Eventually you get a surface looking good; you want to see consistent scratches in both directions. There will be obvious low spots; they still have a shiny un-sanded look. These were located around the recess on this bulb.

First I draw around the lows, and then using a small sander, carefully scuff the shiny surface in the "dents". You NEED to scuff the shiny surface or the fairing won't stick 100%. Drawing around the spots makes sure you don't loose their location after the scuffing.

Filler gets applied carefully in the scuffed area; the surface around the dents is fair and you want to avoid sanding into that surface. Don't apply a big lump that's difficult to fair without getting into the surrounding surface - you may need to do an additional fill after. Fairing the spots will eventually revel the lines you drew; that's when you know it's time to stop sanding.

View attachment 565289
I like to to use a slightly thickened resin (cabosil and black pigment) to coat the bulb after I think it's pretty good. The cabosil keeps the resin from sagging, and if you're lucky, self levels beautifully. The black/shiny surface reveals anything that looks odd.

Looks pretty good . . .

It looks amazing! It's so cool watching it near completion

 

[Steam Flyer]

If I made anything that perfect, I'd be looking over my shoulder for some jealous god smiting me

 

[Jim Donovan]

Got my drill guide tube in the mail the other day, 3/8" O.D. x 0.259" I.D., cut three pieces and inserted into the 3/8" holes in the recess plug. This gave me a 2.5" long drill guide for the initial 1/4" drill.



The holes are about 6" long through the bulb - using some cutting oil made this a very easy process - just had to clean the bit of lead every 1/4" or so. The extra 0.009" on the guide tube, coupled with the oil prevented the bit from binding and helped get the lead shavings extracted.

After drilling (3) 1/4" holes, I removed the drill guides and went through with a 3/8" drill bit.
The holes in the recess plug definitely helped guide the bit and the 1/4" hole guided the bit straight down the hole.



Not concerned about a perfect fit; the bolts are there to hold the weight of the bulb into the recess. Transverse and longitudinal loads are handled by the fin in the recess.

The recess is tapered so the fin will wedge in tight as the bolts are tightened.

Considering opening the holes a 1/16" so the fin threaded rods will slide in easier. Just need to find a 7/16" x 12" bit. Long drill bits are a fact-of-life in boat building . . .

 

[Jim Donovan]

Assembled and shaped the "packing" that fills the keel box at the upper end of the keel. Originally I thought I'd cast it with resin/milled fibers, but that'd be too heavy. Thought about Coosa-Board, but the small amount I needed is impossible to source. So looked around at was available in the shed and made a foam cored panel with 4 layers of carbon each side.

Cut C-shaped parts and made a sandwich of those parts; the packing is about 7.5" tall.

 

[Jim Donovan]

Then I got the nerve to cut the kelp cutter slot in the leading edge tube; You can't F that up or you're into about a weeks worth of rework. I've done this before and have the perfect tools for it; the Dremel saw is awesome and the blade width is perfect for this task. It was not nearly as dramatic as I imagined, and the cut went perfectly (looks less than perfect in the photos due to the peel ply).



The kelp cutter uses a carbon tube that'll have a steel blade attached

 

[Jim Donovan]

Ready to cast the lower end of the fin into the bulb tomorrow morning (after heating resin for a couple hours) Nice to see the laser shoot straight up the kelp cutter slot (the green beam is shooting onto the backside of the L.E. tube).

 

[Jim Donovan]

Like the shiny black bulb and probably going to clearcoat the fin. The fin still has peel ply on it below the orange masking tape, so not as pretty as it will be. The bottom of the masking tape is approximately the bottom of the hull, so you can see this is a "serious" keel fin. The boat will draw about 5'-8"; if we're dragging 620lbs of lead around I want to make sure it's working. The rig's a Melges 24 mast, and we have a fathead main; I think we're going to like this fin/bulb combo . . .

 

[Jim Donovan]

 

[Jim Donovan]

The outdoors temp has been pegged at 23 F all day.
Got the heaters going a couple hours in advance; heating both the resin and bulb.

Jammed and waxed some 3/8" diameter dowels into the lower end of the keel fin, waxed the recess in the bulb, and then poured a resin/milled fiber mix into the recess. I hope the wax works or I've just glued the fin to the bub forever . . .

 

[longy]

Nothing is forever - you just need a bigger hammer

 

[Varan]

Aren't laser levels great

 

[onedesignj80]

View attachment 567354

Jim, How much runner load do you anticipate going downwind in 20 tws?

 

[Jim Donovan]

In twenty knots of wind, this boat will be averaging mid teens, so apparent wind speed will be single digits. Topmast backstay loads will be "not much".

 

[Jim Donovan]

Aren't laser levels great

This cheap laser level seems okay - the beam's plenty bright but a bit too wide; have a Bosch laser level on my wish list.

 

[@last]

In twenty knots of wind, this boat will be averaging mid teens, so apparent wind speed will be single digits. Topmast backstay loads will be "not much".

Will be interested to see the on water shots this spring/summer. Boat looks pretty powered up on paper so imagine it will be a thrill ride. Thanks again for all the pics and reporting, it helps those of us who live in a northern clime think about the upcoming summer on the water.

 

[Jim Donovan]

Picked up the entire bulb with the chain hoist until I put my foot on it and it came loose.
Looks good