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Vessel Name: Wine Down (Albin 28 TE); Bull Dolphin (Bowen 28ft Pirogue)
Engines: Yanmar 6LP-STP ; twin Suzuki DF140s
Location: Consett Bay
Country: Barbados
I know Tony has a nice article which mentions some of this @ “https://www.sbmar.com/featured-article/everything-you-need-to-know-about-marine-exhaust-systems/” but I am still not 100% clear.
I have a 4” hose coming off my yanmar 316 6lpa mixing elbow (aftermarket cast 316 stainless, but identical to oem part in dimensions). So, this exhaust hose inside diameter is 4”.
If I install a lift muffler after this hose, therefore the outside diameter of the fiberglass tube inlet to the lift muffler should therefore be 4” also.
Now, I do see lengths of fiberglass tubing online, and 4” fiberglass tubing has OD 4” and ID of around 3.73”.
Now, I am in Barbados, and it is probably a lot more cost effective to make my own fiberglass tubing (in order to make a lift muffler). I thought it would be as simple as buying the correct size PVC pipe, and using that as a mold to make the fiberglass pipe, but it looks like I would have to buy a 3” pipe (OD 3.5”) to use as a mold and build up a 0.5” wall thickness of csm/stitch mat to get back to the 4” I need for the hose to go over. Now this should then be nice and strong, but then I might be adding some additional back pressure with my exhaust effectively going from a 4” hose to a 3.5” inlet (even if it is only for a foot or so journey each side of the lift muffler)Any comments or thoughts on this?
I have been looking at a few local boats for design ideas, but all systems I have seen are locally made, and a majority just use schedule 40 pvc pipe for the exhaust, so I am a bit skeptical of these, and want to ensure mine is bullet proof.
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You might want to consider running the exhaust out the side of the engine room, rather than all the way to the transom.
The shorter run will maximize the available drop, decreasing chances of backflow.1 user thanked author for this post.
PE resin shrinks when it cures. It will very difficult to get this off your PVC mandrel no matter how much wax you use. Pony up and buy the fiberglass tubing.
D
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Just an IDEA
Since you are thinking makeing your “own”, the OD of a 4″, 5″ or ??” SQUARE section has measurably more internal area than a round section.. Just short round transistons is all you need.. Plus, way easier to lay up..
2 users thanked author for this post.
How much fiberglass pipe do you need?
I need about 24 feet! or less if I combine hose for the accessible areas in the engine room and fiberglass pipe only from transom to engine room along side the fuel tank. Need to measure more precisely to make decisions.
I agree with you that using pvc as the exhaust tube itself (fiberglass wrapped or not) is not the right way.
Definetly make your own if importing is not an option, buy using the pvc pipe or any rigid pipe only as a mold. I’ve done it by:
1. Laminating one layer or two (depending of cloth weight) around the pvc pipe.
2. Cutting the glass lengthwise (with a utility knife) on the tube after resin is set (or still green is easier), using a straight edge, (does not really matter if its super straight or not.
3. Wait for full set, next day and … Releasing and removing the fiberglass shell from the pvc mold.
4. Glassing this fiberglass shell/thin tube to desired specifications (thickness).
I did not use CSM (mat), only 0-90 cloth, haven’t tried stitched biaxials over a pipe yet.
CMS adds bulk fast but is not as dimensionally strong as cloth for same thickness. All depends on your needs as thickness will always be stiffer than thinner material, and plenty strong for this scenario. Perhaps combining CMS and cloth or combo or biaxials will get you where you need to be without doing 300 layers of 1oz cloth hehe.
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Hi Gary,
Im having a similar dilemma on fiberglass tube options to reduce the 12 foot sections of hose I have from my 6BTAs to the transom, 24 feet total roughly.
6″ hose is almost non existent in 12 foot sections, its also super expensive if found and shipping to the Caribbean would cost as much as the hose.
Looking to either buy fiberglass tubes or make them like you said over a pcv pipe mold.
I’ve done this before at a smaller scale with 3″ pipe. Just time a couple of weeks after work, effort, materials (PE resin, 12ounce cloth roll) and patience. Guessing materials would be under 500$ everything else is time and effort on my part.
I have a post on this, pending replies. If you can check it out “6BTA Wet Exhaust Hose Constraints and Options?”
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Tubing is actual OD. 4″ tube is 4″ OD Wall thickness does not affect the OD dimension.
Pipe size is a nominal OD ( 3″ pipe is 3.5″ OD, 4″ pipe is 4.5″ OD, 3.5″ pipe (hard to find) is 4″ OD Schedule and the material does not matter on the OD measurement, only the ID.
Making your own tubing–Labor must be free to do that
Will it work? …………… I’m sure it will “work”-
Will it meet exhaust pressure spec?- Probably not even close.. Does that really matter?
……………….. No comment…1 user thanked author for this post.
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