Tips on cutting centerboard slot

[zumwaltd]

I am looking for advice on when I should cut the centerboard slot on my Belhaven:  Is it easiest to cut out the slot before turning the boat over or after turning the boat over?   Before fiberglassing the bottom or after fiberglassing the bottom?  I am having trouble figuring out the building sequence that would best help me make an accurate cut.  It seems to me I could make a more accurate cut prior to rolling the boat over but that may make fiberglassing the hull more problematic. From the build pictures I have seen I am not sure which way I should proceed. 

Thanks in advance for your suggestions.

 

Dave

[wkisting]

My preference was to drill a small locator hole in the hull right where the centerboard would eventually sit. Then I glassed in the CB case. Then I flipped the boat. Once the boat was upside down, I widened the locator hole carefully, and inserted a router with a flush trim bit. Then I taped sticks onto the bottom of my router base to hold it at the correct (perfectly vertical) angle and cut out the slot. The bearing on the end of the flush trim router bit rides the inside of the (installed) CB case and cuts an exact matching slot in the hull.

 

One other tip... before installing the CB case, I cut a piece of wood the exact thickness of the centerboard, wrapped it in packing tape (to prevent epoxy adhesion) and stuck it up inside the case to make sure the case width stayed correct as I installed it. I also pushed it a few inches up from the bottom to make sure there would be plenty clearance for the router bit when I cut the slot. Once the slot is cut, you can reach up into the case and get the spacer block out again (or you can wait until you flip the boat back upright and take it out through the top of the case--whichever is easier.

[Howard]

Not sure on the build sequence for the Bellhaven. Scott would know better than most.

 

For the Princess, which is formed upside down around the bulkheads, my plan is to form the sides and bottom over the bulkheads, turn her over.....then install the sheer clamps (inwhales) and tab the bulkheads, then cut the centerboard slot and install the actual CB trunk........which runs parallel to the centerline of the boat........then turn her back over to glass the hull, glass the CB slot and install the keel stub.

 

For the Princess, ideally, you need the CB finished first, so you can add just enough width to the king posts to set the width of the CB trunk and CB slot, so the board will fit in with the desired tight tolerances. I suspect the Bellhaven would work the same.

[Chick Ludwig]

I agree with wkisting. I only turn the boat once. While it is upside down, I do everything on the bottom including paint.One additional note. After cutting the slot, round over the edge. Glass over the corner into the trunk with a layer of 10 oz. cloth tape. When cured, feather the tape edge and then apply your glass that is covering the bottom. Before wetting it out, cut a slot down the length of the opening through the glass so you can roll the glass over the edge. Proceed with wetting out the glass and finishing as usual.

 

[wkisting]

Yep, forgot that bit Chick mentioned... after the flush cut bit, I used a 1/4" roundover bit to round the edges around the CB slot, then when I 'glassed the bottom, I cut a slit over the CB slot and wrapped the glass up inside the case. I also went back and lined the case edges with a second layer of glass (using 3" wide fiberglass tape), then blended it in. Came out great.

 

Just be sure to use a long thin board with sandpaper stapled to it to sand up inside the slot afterward so there's no worries about sharp fiberglass edges wearing against your board. Then a foam brush dipped lightly in epoxy will allow you to put a final seal coat on after sanding.

[Charlie Jones]

And I do exactly what Chuck and Wkisting do, using a flush trim bit, then a round over

[zumwaltd]

I am really pleased I posted my questions.  Thank you for your responses.  They were just what I needed to 

help me understand how to approach this task.

 

Dave .  

[Tom Lathrop]

And I thought I invented that method that Wes, Charlie and Chick use.  I've done all of that for many years and see no reason to change.  One other thing I do is to line the bottom of a daggerboard trunk with felt of sufficient thickeness to grip and hold the board in place while allowing it to be adjusted.  That was brought home last Saturday when I was on the RC boat for a Sunfish race in 20 to 25 kts.  All of them capsized and one had so much trouble that he had to retire.  His daggerboard kept falling back in the trunk when he tried to get to it with the boat inverted.  Many use a shock cord attached to the mast to hold the DB but the felt is better and is always there.

[maligno]

Dave, 

 

How successful were you in making the 1/4 ply doubler lie flat against the bottom panel where the CB box goes? 

 

I wasn't with mine and there's a gap of up to half an inch between the doubler and the bottom panel, so I'm considering cutting out some of the doubler around the centerboard slot but that will make it difficult to fit the bottom curve of the CB box. It may be easier for me to push the box right through the hull and then fair it outside.

 

If I were to do it again I'd lay the doubler in strips after the CB box and the longitudinal bulkheads are glassed in.

[zumwaltd]

Rolando,  I think my doubler came out close to what the designer had in mind. Not perfect but close.  See pics.

[maligno]

It does look better than mine