Sorry to bring this up again, I have read all the past threads and I am about to begin the cave hatch project. I plan on only making a 24 x 30 hatch (smaller than most of you have done). Just to access the shower pump and most important to replace my 24 year old hot water heater (16 x 16 x 16). I plan on putting back only a 6 gallon hot water tank (which was enough capacity on my last boat). I feel the size of the head holding tank is adequate and if I did change it I would access it thru the cave entrance.
I see most of you have used a circular saw for the cutting of the floor. My thought was to use a router, but have never used one on fiberglass before, second choice you be a fine tooth jig saw, any thoughts on this.
I would use a circular saw to cut the long cuts and a jig saw to finish the cuts in the corners. Use a wide piece of plywood as a straight edge to run the saw against and you will get a nice cut. Have someone stand on it to hold it in place or maybe use some two sided (Thick) carpet tape.These saws only remove an 1/8" wide (or less) amount of material.
If you used a router, you would need to use a much wider cutter and that might leave the cut out with too much play from side to side. Should you decide to use the router, then make a jig out of plywood and use a collar on the router base to follow it with. You will need a long plunging bit to make the cut. You might get away with a 1/4' bit if you took multiple passes to make the cut. Drop the bit about a 1/4' in depth for every cut until your through the decking.
I personally would use a 3/8" wide bit. The problem with 1/4" bits is that they tend to break in deep cuts if they bind. That's why you need to step the cut down slowly when using them. A 3/8" bit will take a lot more stress and make a deeper cut without breaking. I think you will need to be able to cut through about an inch of wood and fiberglass. I would also screw a couple strips of wood to the bottom side of the area to be cut out. Have the ends screw to the outside of the cut and put a couple screws into the part that will be cut out. This will keep the cut out piece from shifting during the last cut and binding on the bit. It will also keep the piece from crashing into the cave.
I would like to suggest that you consider replacing the hot water heater with the same size, 11 gal if I remember it right that came from the factory.
Not only might your needs change in the future, but also think of reselling it to the next owner, who might wish it had a larger hot water heater.
Its unlikely you would lose the sale of your boat to another comparable because you have a smaller water heater, but why take the chance.
In my opinion, when doing modifications to your boat, you keep it same as factory or improve its capacity/capability. Not diminish it...
You might also reconsider the size of the opening. Even though your holding tank may be ok now, at some point you will want to replace it or the hoses and a larger opening will make the job a lot easier. I'm not sure what size my opening is, but the holding tank will fit through it. I can see no down side to a larger opening and the effort to install it is about the same. Good luck,
I made this modification on our 32. I would suggest that you rethink the size. I made mine actually a little larger than most. Getting the lines off and the old tank out was a chore even then. You need to move the tank to access the water heater. I ended up having to use the hatch to access the wire runs also.
If you are worried about making the floor week, don't. That was my original concern but after I made the ring for the underside of the opening to support the hatch and secured it with two rows of screws and 5200 all around the floor is as strong if not stronger in that area because of it.
If you are not comfortable with a circular saw and plunging, use guide boards to ensure a straight cut. The cleaner the cut the better the opening will look afterwards.
I use a circular saw on the straight cuts and a reciprocating saw on the radiused corners. The blades are sufficient different in side and required a lot of clean up. If I were to do it again I would make the cuts straight and square the corners.
Be careful with your measuring as there are a lot of things under that floor. I used blue masking tape the deck to do my layout work on. It helps to protect the fiberglass from breakout during the cutting and if you make a mistake in the layout just pull up and start over.
One last piece of advice unless you ask for more, you have heard the term measure twice, cut once. Well when it comes to this cut I would suggest measure about a dozen times as you only get one chance. I found it helpful to sit and stare at the layout with a beer for awhile to see if I had overlooked anything and pictured doing the deed to see if there was going to be any problems with making the cut.
What I am trying to say is plan carefully and take your time.
You will love this modification as you will access this area more than you thought once it become accessible.
Ron, I just did this modification last weekend on my 3288, don’t go too small, mine is 24 X 40. I read Pat's write up 10-15 times before I started. He's right; you should use a circular saw for the straight cuts. I put a small radius, 1”, in the corners because I think that a square corner will create a stress point and a starting point for cracks. Next I will be changing out the whole sanitation system, water pump and the macerator. This is a great modification. I posted some pictures of mine and I know Pat posted his along with a great right up. Check under “Completed Projects” good luck.
I still don't get it. I can get to all the sanitation hoses from the cave entry (changed them already) . If I had to change the holding tank that also would come out the cave entrance. For me the main reason for the hatch would be to change the hot water heater. That being said why didn't you start your cut-out closer to the the helm station for better hot water heater access?
I used a sabre saw with a metal cutting blade. I was careful and made a nice clean cut. I think mine is 24 X36. It is far forward in the cave. I also countersunk my hinges to keep the cabin floor flush under the helm chair. Be sure to have a way to secure the hatch in the up position. It is very heavy and could hurt if it fell over on you. I had an engine hatch cover do that once and for awhile I thought I got a broken arm out of it. I used a spring assembly used on similar marine hatches.
You will find that access to the heater is a one time shot in most ownership life. Access to the holding tank and other things in there may be more frequent. For this reason most of us have position the hatch back so that it just misses the hot water tank. If you place it forward you will have to remove the hot water tank to do virtually every thing in that area.
If you look up my posts you will find all of the measurements from the foreward wall and from the side (Stbd) wall. The Stbd wall is not perpendicular to the front wall but the bulkhead in the cave is. I cleared this wall by just enough to install the support ring.
Mine is further forward, because it opens up the areas that I can't reach from the cave.
It's also longer. I don't have the dimensions - but my thought is that the purpose of doing the work is so you can remove / replace kit in that part of the boat easier ( not necessarily easily ). Put mine in after having to replace the macerator - which is probably the weakest link in all the kit installed down there.
While you may not need to remove the hot water tank through the hatch, getting at all the plumbing fittings easily is well worth the extra size.
Mine was done by a boat-builder - I'm just unable to cut straight lines with any kind of saw. But it was a quick job for him.
I did use the dimensions given on the site to ensure clearances for both the front & starboard cuts.
That's probably the most important piece of information.
I bought a hatch kit from Boater's Discount Center in La Conner a number of years ago. See photos below. It came with a template plus a fiberglass piece that supported the hatch. In order to replace the hot water heater I had to pull out the holding tank which wasn't too difficult. I think a hatch is a necessity to access items such as the holding tank, water heater, fresh water pump, etc.
My hatch is 24X36, located 5" from the starboard wall. I have a smooth seam in the floor texture that runs perpendicular to this wall, back about 48" from the helm bulkhead trim. My rear cut is in the middle of the seam. Just thought it would look best there... So my forward cut is about 12+ inches back from the helm bulkhead trim. I located here because we have built a footrest/vessel documents box that comes back about 12" from the helm bulkhead trim. Looking closer at it tonite, I would have to slide my holding tank rearward about 8" to get the water heater out, so you may want to locate your hole farther forward. If you want some pictures, send me a message. I don't quite have them in my computer right yet to post (computer challenged).
The floor is about 1+" thick. Depending on your saw, you could produce alot of flying dust and fiberglass particles. That's a big reason I used a sabre saw with a metal cutting blade. I drew a fine line and closely watched my cut, staying right on the edge of one side of the line. I also had my shop vac hose right next to where I was cutting to suck up the dust particles. To work with hinges, I actually had to bevel the non-hinge side of the door, to freely clear the hole.
BEWARE: Make a fiberglass dust mess of the cabin and the Admiral WILL NOT be happy. You don't wanna go there!:oop-
Yes I finally did it after owning the boat for 9 years I cut the hole! It was very stressful, made a couple of small pilot holes first, then hit it with a jigsaw. When I finally popped out the piece and saw the access, one big smile and said to my self (like everyone else that did it before me) I can't believe I waited all this time to do this. Installed a support ring bondo putty the edges, painted the cave area (not completed) and installed the new hot water heater. Will gel-coat the edges this fall as the season winds down.
I know this is an older thread but I'm going to make this mod on my 3270 shortly.
What type of circular saw blade should I use to make the straight cuts?
Some said they used a reciprocating saw. My plan was to use a jig saw for the rounded corners. Would a laminate floor blade be best as the teeth point downward or what is recommended as to not splinter the finish floor? Metal cutting blade?
I plan on using 3/4" ply for the ring. Would 1 1/2" flat hd screws be sufficient so as not to go through the cabin floor?