As with anything like this, there probably is a whole variety of workable solutions. This is how I made my access water tight (in normal conditions anyway).
Firstly, picture #01 is the engine access hatch -- for those interested what I'm describing, but don't have a Cherubini Hunter 36.
Now for a description of my mod.
The fastener combo is in the attached picture #1. The thread size is 10-24. (But 1/4" x 20 might actually be a better choice because of less chance to cross-threading with repeated use.) The barrel nut is inserted up through bottom as in picture #2. Points of note for the fastener system:
- Make straight one side of the round bottom flange of the barrel nuts by grinding/filing and also rough up the barrels with sandpaper so that it won’t later spin in its epoxy “cocoon” -- which is described further below.
- Find a drill bit that matches the outside diameter of the barrel nut. Drill out the existing screw holes in the cockpit deck, using a bit that will allow the barrel nuts will fit in snuggly. At this time, ensure that the underside of the cockpit deck around the holes is clean. Suggest acetone and roughen the areas with sandpaper.
- Insert the barrel nuts from the bottom up, again as per picture #2. Align the top of the barrel nuts (the open threaded ends) protruding just above the deck level - say about 1/16"
- Also align them straight vertically.
- From the top, between the joints of the barrel nuts and deck screw holes that they are inserted into, run a bead of runny super glue. Runny type (not the super glue gel), so that the glue penetrates into the small gaps in the joint. Don't get the glue into the interior of the barrel nuts. This super glue step is needed so that the barrel nuts are firm and don't move around when doing the next step.
- This step is best done with vinyl gloves so that you can "feel" your way with your finger tips. Using a good quality thickened epoxy that dries rock hard (not rubbery like the 5-minute type) and is of the consistency of soft putty (very easily moldable, but won't drip ), pack the epoxy around the bottom of the barrel nuts so that they become covered with epoxy "cocoons" mated to the underside of the deck flange. Squeeze the epoxy well with your fingers to ensure that the epoxy is worked in tight around the barrel and pressed up against the underside of the cockpit floor deck. See picture #3. Be careful not to break the super glue seal while doing this step. Probably two applications of epoxy are best.
- Now you have a durable and reusable female thread. Whenever the hatch is removed, the 10-24 screws can be removed and replaced over-and-over again. Also the joint won't leak water!
- From the top, and again referring to picture #1, you can see the combo of washer and faucet washers that I used to also aid in preventing water from getting through. However, with the set-up of the main gasket (the black perimeter thing in picture #6) this probably isn't necessary. Just a flat head 10-24 screw and a flat washer probably will do.
- Select a length of 10-24 screw that will go well into the barrel nut, but not bottom out before the gasket (described in the next section below) is compressed. Also on this point, the longer the length of "barrel" of the barrel nut, the better.
- The area around the screw holes in the hatch cover top between the smooth gelcoat and the non-skid suface need to be made flat so that the screws and washers will seat square. See picture #4. I used a Dremel fitting to do this. The fiberglass in this area is thick enough that I did not expose the wood core. But be cognizant of this possibility. If so, seal the breach with epoxy. Another item: It is possible that the location of each hole in the hatch cover won't align exactly with its mate underneath (as was my case). So these holes need to be enlarged a bit -- the reason why flat washers are needed.
Now to the gasket part:
See pictures #5 & #6. I can't remember exactly what size of press-on gasket material I used -- and it is now squished flat. Probably 1/2" x 1/2". The gasket needs to be good grade and dense foam -- not the light stuff from home-improvement centers. You will need to make your own determination of the exact location to apply it so that is will match up with the deck side's raised flange. Obviously, you need to remove all traces if previous caulk attempts. Acetone will be needed to remove residue of silicone, or the new press-on gasket won't stick.
Note in the picture #7 of a hatch bottom hole, I added little bumpers on each side of each hole. This was to prevent bending the hatch cover flange with each tightening and to prevent over compression of the gasket.
I also found that on the fore and aft edges of hatch cover, the flange bent down too far and would contact against the deck before the gasket was engaged. See picture #8 showing that I needed to grind off some material.
In the picture of the bottom of the hatch cover you might be curious about the wood strip and the aluminum sheeting. The wood strip makes the cover a bit more rigid -- doesn't feel springy any longer. The aluminum is actually press-on sound deadener material, normally used in cars to deaden panel resonance. I've applied this to various panels/bulkheads around my engine compartment. The noise level in the cockpit from the reliable, but really noisy and shaky 2QM20 has been noticeably reduced.
Hope all this give you some ideas for you own solution!
Firstly, picture #01 is the engine access hatch -- for those interested what I'm describing, but don't have a Cherubini Hunter 36.
Now for a description of my mod.
The fastener combo is in the attached picture #1. The thread size is 10-24. (But 1/4" x 20 might actually be a better choice because of less chance to cross-threading with repeated use.) The barrel nut is inserted up through bottom as in picture #2. Points of note for the fastener system:
- Make straight one side of the round bottom flange of the barrel nuts by grinding/filing and also rough up the barrels with sandpaper so that it won’t later spin in its epoxy “cocoon” -- which is described further below.
- Find a drill bit that matches the outside diameter of the barrel nut. Drill out the existing screw holes in the cockpit deck, using a bit that will allow the barrel nuts will fit in snuggly. At this time, ensure that the underside of the cockpit deck around the holes is clean. Suggest acetone and roughen the areas with sandpaper.
- Insert the barrel nuts from the bottom up, again as per picture #2. Align the top of the barrel nuts (the open threaded ends) protruding just above the deck level - say about 1/16"
- Also align them straight vertically.
- From the top, between the joints of the barrel nuts and deck screw holes that they are inserted into, run a bead of runny super glue. Runny type (not the super glue gel), so that the glue penetrates into the small gaps in the joint. Don't get the glue into the interior of the barrel nuts. This super glue step is needed so that the barrel nuts are firm and don't move around when doing the next step.
- This step is best done with vinyl gloves so that you can "feel" your way with your finger tips. Using a good quality thickened epoxy that dries rock hard (not rubbery like the 5-minute type) and is of the consistency of soft putty (very easily moldable, but won't drip ), pack the epoxy around the bottom of the barrel nuts so that they become covered with epoxy "cocoons" mated to the underside of the deck flange. Squeeze the epoxy well with your fingers to ensure that the epoxy is worked in tight around the barrel and pressed up against the underside of the cockpit floor deck. See picture #3. Be careful not to break the super glue seal while doing this step. Probably two applications of epoxy are best.
- Now you have a durable and reusable female thread. Whenever the hatch is removed, the 10-24 screws can be removed and replaced over-and-over again. Also the joint won't leak water!
- From the top, and again referring to picture #1, you can see the combo of washer and faucet washers that I used to also aid in preventing water from getting through. However, with the set-up of the main gasket (the black perimeter thing in picture #6) this probably isn't necessary. Just a flat head 10-24 screw and a flat washer probably will do.
- Select a length of 10-24 screw that will go well into the barrel nut, but not bottom out before the gasket (described in the next section below) is compressed. Also on this point, the longer the length of "barrel" of the barrel nut, the better.
- The area around the screw holes in the hatch cover top between the smooth gelcoat and the non-skid suface need to be made flat so that the screws and washers will seat square. See picture #4. I used a Dremel fitting to do this. The fiberglass in this area is thick enough that I did not expose the wood core. But be cognizant of this possibility. If so, seal the breach with epoxy. Another item: It is possible that the location of each hole in the hatch cover won't align exactly with its mate underneath (as was my case). So these holes need to be enlarged a bit -- the reason why flat washers are needed.
Now to the gasket part:
See pictures #5 & #6. I can't remember exactly what size of press-on gasket material I used -- and it is now squished flat. Probably 1/2" x 1/2". The gasket needs to be good grade and dense foam -- not the light stuff from home-improvement centers. You will need to make your own determination of the exact location to apply it so that is will match up with the deck side's raised flange. Obviously, you need to remove all traces if previous caulk attempts. Acetone will be needed to remove residue of silicone, or the new press-on gasket won't stick.
Note in the picture #7 of a hatch bottom hole, I added little bumpers on each side of each hole. This was to prevent bending the hatch cover flange with each tightening and to prevent over compression of the gasket.
I also found that on the fore and aft edges of hatch cover, the flange bent down too far and would contact against the deck before the gasket was engaged. See picture #8 showing that I needed to grind off some material.
In the picture of the bottom of the hatch cover you might be curious about the wood strip and the aluminum sheeting. The wood strip makes the cover a bit more rigid -- doesn't feel springy any longer. The aluminum is actually press-on sound deadener material, normally used in cars to deaden panel resonance. I've applied this to various panels/bulkheads around my engine compartment. The noise level in the cockpit from the reliable, but really noisy and shaky 2QM20 has been noticeably reduced.
Hope all this give you some ideas for you own solution!
