Here is the 6" exhaust profile for the side exhaust at the 22.5 degree turn to come out the side.
Here is the actual drawing on the hull after removing the profile piece.
I had originally thought I would simply make a jig for my router to cut through the hull side like Capt. Pat supplied with the dorade boxes he sold. However, the bottom of the cut will be made on the uneven section where the chine pushes out.
Is a jigsaw the best option here? If so, any recommendation on type of blade and speed while cutting?
John,
I've always used a jig saw with a metal blade for most of my work. The metal blade ( bosch T111 or T118 comes to mind) doesn't do the damage that a wood blade usually does.
I would cut about 1/8" inside the line, then angle it with a dremel tool. You will be amazed how much a dremel can eat up with a small barrel sander bit.
In a nutshell, the whole issue started with my desire to have in deck fish boxes and how best make an exhaust run outside of the outboard stringers.
The primary issue with creating the space for in deck fish boxes and moving from 5" to 6" exhaust thru hulls outside of the outboard stringer is Shambala's outboard swim platform supports would have to be relocated slightly inward to take a 6" fiberglass exhaust tube through the transom and fair the outside section to the transom. The same would have been true if I had used 6" bronze thru hulls
The other issue that concerned me was the possibility of surge from the additional straight shot of exhaust hose potentially creating more momentum from water heading into the exhaust hose from the slightly higher and 1" larger thru hull.
In a nutshell, the whole issue started with my desire to have in deck fish boxes and how best make an exhaust run outside of the outboard stringers.
The primary issue with creating the space for in deck fish boxes and moving from 5" to 6" exhaust thru hulls outside of the outboard stringer is Shambala's outboard swim platform supports would have to be relocated slightly inward to take a 6" fiberglass exhaust tube through the transom and fair the outside section to the transom. The same would have been true if I had used 6" bronze thru hulls
The other issue that concerned me was the possibility of surge from the additional straight shot of exhaust hose potentially creating more momentum from water heading into the exhaust hose from the slightly higher and 1" larger thru hull.
John
You might want to talk with Bob Lilco. Over the weekend he was explaining to me how the muffler he used has a baffle that prevents water from running past it so no surge tube required. Not sure it would work in your application but an option.
Jig saw with an abrasive / ceramic blade. Fiberglass heats tooth blades to the point of failure quickly, but the abrasive blades last a long time. May be difficult to deal with the reverse chine trying to use a jig saw. I have a large 20,000 rpm end grinder that I use a lot with carbide burrs. The high quality burrs for that thing run $40 bucks a pop.. don't use cheap ones, they fly apart at 20K. I typically cut under size with anything that will fit the bill. Then I come back with the 20,000 rpm end grinder and do the finish (fine) work going exactly to my scribe line. You could use a Dremel tool. Small circular disc to cut out (under size) and finish with a 1" flapper wheel.
Scot
1969 Bertram 25 "Roly Poly"
she'll float one of these days.. no really it will :-0
Jig saw and I like Barrel Sanders using a drill to open, move, elongate holes.
Flap wheels are great to keep hole round-ish and smooth...but slow to cut.
Bigger, course cut are easier to keep contour smooth and they stay cooler at low speeds.
At Knuckle Buster Central (AKA- Harbor Freight) they are dirt cheap and work as well as the ones I get from my industrial supply house.
When you post a reply and you hit the "submit" button, a new screen appears where you probably read "your reply has been posted successfuly", or something along these lines.
If you wait a few seconds you will see your very post appear within the thread in question.
However, if you RUSH and tap on "Board index" on top, BEFORE your post appears by itself, then the post disappears !
Magic!
Ask me how I know !....
If water surge up the exhaust is a concern you might want to consider this: a 28 has a tendency to roll a little bit on the drift. I have, on a few occasions when I should have been somewhere else, actually rolled enough to have water hit the rubrail. It is common to have water climb halfway up the hull sides as she rolls. That oval opening you have laid out on the side looks sharp, but it is a damm big opening to push 12 to 24 inches under the water every few seconds. Of course a transom opening is pretty big also, but water isn't being forced into it from the side as the boat rolls.
Maybe the mufflers can stop the surge. I hope you can work it out, because that side exhaust does look good!
Tooeez wrote:If water surge up the exhaust is a concern you might want to consider this: a 28 has a tendency to roll a little bit on the drift. I have, on a few occasions when I should have been somewhere else, actually rolled enough to have water hit the rubrail. It is common to have water climb halfway up the hull sides as she rolls. That oval opening you have laid out on the side looks sharp, but it is a damm big opening to push 12 to 24 inches under the water every few seconds. Of course a transom opening is pretty big also, but water isn't being forced into it from the side as the boat rolls.
Maybe the mufflers can stop the surge. I hope you can work it out, because that side exhaust does look good!
Yannis
The issue of water surge occurs when backing down fast on a fish, and depending on how the boat lays into the waves, if you get a wave hitting the stern and before I forget, if you hot rod and then throttle back all the way in one shot the stern wave catch's up with you and can run up the exhaust.
That being said, the right down angle on the exhaust leaving the engine and running aft, mufflers and engines high enough might be enough to stop it.
I do not have surge tubes and have mufflers. Knock on wood I have never had an issue.
Did u ever decide on whether u are going to do the side exhaust. I wrote a long narrative but somehow lost it.if u are still interested ,I'll write it again.it was the play by play that Capt pat coaxed me thru when I did mine
I have never heard of water running up an exhaust with the engine running--I don't think the force of the water entering could overcome the force of the exhaust exiting, unless the water pressure completely blocked the exhaust gas from passing through, which would stall the engine immediately. I do know of several boats (none of them Bertrams!) that experienced water intrusion through the exhaust while drifting in rough conditions with the engines off, and one case of a fairly large vessel tied to a pier stern to a 30 knot wind having the waves striking the stern drive water into both engines.
i am not going to explain motive or reasoning just facts, lets say it behoved me to slug my cummins 6bta engines and acquire a set of QSB cummins. i back down as fast as the boat would go without going sidewards with quite a bit of white water coming over transom somewhat dangerous at a point. the engines refuse to take water ,afterwards realizing no labor for engine transfer given it was not worth it to destroy perfect engines. be it as it may the mini max mufflers cannot be by passed by a surge of water leading me to make the statement "surge tube/vernatone muffler combination with the lost of precious engine compartment room for generator,waste tank " bad move let it go!
Hole saw, the best way to go.
No it's not a straight cut, you will cut at an angle and possibly a compound angle, therefore you will have to make a scraficial block. The block will be square with the pilot drill bit and the saw blade teeth. Once you get into the glass. You can remove the block. Also if you can't find a hole saw deep enough, build up the block with layers of ply wood screwed together, you can remove each layer as you get deeper into the block and hull. This will be the cleanest hole and best matched to the diameter of your pipe. You can screw the block to the hull through the hole center waste. Very easy and safe, just oscillate the blade so you don't bite 360 degrees of material at once.
Best of luck!
"Some of its Magic, some of its Tragic", Jimmy Buffet
Bertram 35 "SeaDuction”
Bertram 31 Project
Bertram 25 Project
Bertram 20 Baron Project
Florida Panhandle
Once I cut the hole with a special saber saw blade for cutting f/g( Lewis marine) I ground the tapered area per the Capt,s formula, 12x the wall thickness( .250" x12 = 3 inches taper. I cut donuts out of 1708 biax at this diameter that were also 1" less than the exhaust pipe diameter and slid over the exhaust pipe. I cut 3 more donuts reducing the od /I'd by 1/2" each time and slid them over to check the fit. Removed this sandwich, wet the tapered area of the hul/exhaust pipe with epoxy,rolled each layer with a buble breaker, let every thing kick off, rough ground this exterior mass to get a rough shape with concave 7 1/4" sanding wheels. Mixed up some epoxy with vermiculite till I got a consistency thick enough to form a base ball and forced this over the rough shape and smoothed it out with a shaping tool. Let it kick, sanded. Primed with 545 Awlgrip product, filled with awl fair, sanded/filled a few times till I was where I accepted the product. I also tabbed the inside of the tube/hull with numerous strips of the biax. There were some images of the exhaust pipe /supports and the connections with exhaust hose that isolated any vibrations the engines may have created. 6" f/g tubing for the new 330 hp Cummings QSB engines, also showing how the exhaust tubing was secured. I can't take credit for this methodology, I called the Capt daily,who would have ever thunk about using planting cumpound and epoxy!
After we cut the 22 1/2* angles , we joined the pieces together with 5 minute epoxy to hold /fix them together during the multiple layers of biax. Once it kicked, we set the assy into the hull hole ,aligned the exhaust pipe forward,up/down ,fitted the saddles to hold the pipe,temporarily resupported the exhaust pipe and epoxied in place. The saddles were epoxied latter only to the hull,with a strip of rubber between the saddle and the pipe to absorb vibrations. The pipe was then secured to the saddles by attaching a a retention strip with screws to hold in place. Everything other than the epoxied exhaust to the hull was designed to be revmovable as was the entire deck system. Again ,thx Capt
