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Old 20 December 2011, 16:07   #1
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Inflatable can you fit a self emptying trunk

Hi
Does anyone know if it is possible to fit a self emptying trunk to an inflatable boat.
The type of trunk I am think of is normally fitted to a rib.
I have a large quicksilver inflatable that has a small drain plug but it often fills with sand and does not work effectively.
I guess it is not possible or the boat makers would already fit them as standard.
I am hoping it has been tried and you can tell me how well it works.
Many thanks
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Old 20 December 2011, 16:15   #2
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Quote:
Originally Posted by d1ve1n View Post
Hi
Does anyone know if it is possible to fit a self emptying trunk to an inflatable boat.
The type of trunk I am think of is normally fitted to a rib.
I have a large quicksilver inflatable that has a small drain plug but it often fills with sand and does not work effectively.
I guess it is not possible or the boat makers would already fit them as standard.
I am hoping it has been tried and you can tell me how well it works.
Many thanks
Try speaking to Kieron at Rib Shop he sells these-
http://www.rib-shop.com/prodtype.asp...ageHistory=cat
If you have a solid transom I cannot see why they cannot be fitted
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Old 21 December 2011, 01:48   #3
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Pt. Lobos State Park in California ran a small SIB as a rescue boat; it was about 10 to 12 feet (I'd guess 10) with a small (15hp?) motor and 2 large diameter (4 inch?) elephant trunks. Talking to the rescue guys, they said it wouldn't completely empty the boat (as I recall, the trunks were an inch or two above the bottom of the transom), but went a long ways in getting rid of most of the water after having a swell break over it.

jky
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Old 21 December 2011, 04:18   #4
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It should be easy to fit these- process is no different to a RIB, cut the correct size hole at the base of the transom, seal well and fit. RNLI SIBS have these fitted.
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Old 21 December 2011, 04:22   #5
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Hi yes it will work well just have a look at the SIB’s the RNLA use they have them!

Too slow with my reply!!!
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Old 21 December 2011, 11:09   #6
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You are lucky they are hard to find, make that impossible to find in the USA, but common in Europe. So much so that I have been trying to find a design to copy and just build a set from scratch. It is probably cheaper to buy a kit, then purchasing all materials required.

Are two required in a 4.2m boat or just one? Do you open them after swamping or before if you predict an issue could arise? At what point do you pull them back up into storage position?
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Old 21 December 2011, 12:54   #7
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Peter - try a search for 'elephants trunk' on here - loads of previous how to fit topics etc.
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Old 22 December 2011, 17:00   #8
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Peter - try a search for 'elephants trunk' on here - loads of previous how to fit topics etc.
FWIW I had done the search in the past and did it again last night. Also using "elephant drain", and included a google search. I have quite a few photos saved of boats with elephant drains.

Since the OP and I are trying to accomplish the same thing...here are some specific questions I/we would appreciate any possible help on.

Seems there are no direct answers to my questions available, at least that I can find. I have not been able to find a materials list for DIY which would be my preference.

1: Material for the tube? One person says use Hypalon only, and someone else says "bah", just use PVC.

2: Thickness of material? I already have the two part glue for PVC since my Zodiac is PVC, and it needs to be used up. I even have some PVC, but think it would be too thick. Maybe not, but I am not sure what others use for thickness?? I can buy material, but quickly catch up to buying a kit, if I could locate one in the US.

3: How many drains on a 4.2m hard bottomed SIB? For my boat, the fuel tank is on the port side within a couple of inches of the transom, and therefore would not let as much water out, although still more than not having a tube there. A drain on the starboard side is not as easy to reach since I sit on the starboard tube when driving.

4: Where do you mount the tube? Someone suggested mounting the tube half way between the top and bottom deck? This would drain both but would slow down draining the top deck (Assuming I am only using one). In washing my boat I have found it drains under the deck pretty slowly and I already have a couple small factory scuppers in the bottom of the boat (Usually they are plugged unless we are hauling a bunch of water into the boat with our dive gear).

Photos I grabbed off this site, that shows an above and below deck mount. I think it was an RNLI boat which is designed to be swamped. Hope it is okay to post them by whomever the owner of the photos is.



5: Material for the tube thru the transom? What have other DIY folks used? Something from the local hardware stores plumbing department? Someone found a bronze or stainless item that works? Maybe simple plastic piece? Did you just use a stainless hose clamp to hold the elephant trunk to the drain tube?

6: Size of hole? I have read anywhere from 68mm-70mm for the id of the hole in the transom.

7: For me specifically, does anyone in the USA sell an elephant drain kit for a reasonable price?
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Old 22 December 2011, 18:37   #9
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I just added a single trunk drain to my RIB. I don't have any pictures of it yet. But I am in the States so I will share what I did and why. I saw some kits in the UK and they would ship here, but shipping wasn't cheap, exchange rate wasn't friendly, and I wasn't sure if I would like the tube or if I would be able to find a metric hole saw of the correct size.

My hull is aluminum. The builder recommended two 2-2.5" diameter drains. To be made using an aluminum tube welded to a plate which would be bolted to the inside of the hull with a gasket.

I didn't like that idea because its 2 holes in my transom and 2 would get in the way of my engine, depth transducers and zinc anode which is also on my transom. I also thought bolting an aluminum tube onto an aluminum hull was silly. I bought an aluminum hull for this exact reason, so things could be hard welded.

So I had a single 3.5" hole drilled and a 3" inside diameter aluminum tube welded into my transom. The single 3" diameter hole has a cross-sectional area of 1.5*1.5*3.14 = 7 square inches. Two 2" holes would have been 6.25 square inches. Two 2.5" holes about 9.8 square inches.

Small quantities of hypalon were expensive, and I wasn't sure how thick/pliable they would be. Seems like alot of money to demo it. Instead I bought really thick PVC (1 yard @ $22yard or so in an outdoor fabric store). Glued up a tube of it and boy was it stiff. I decided it wouldn't collapse properly in water. So I went back and got much lighter PVC material and glued up a second tube. Its 10oz /yard polyester reinforced PVC. The tube is attached with dual SS band clamps.

I bought some sailing hardware to hold the cord on the top of the transom.

The last thing I bought was a foam plug specifically for major boat leaks. I figured if the tube fell off or self destructed I could plug the resulting hole with that. Cost at $19 at West Marine but for a giant new hole in my transom it was worth the piece of mind.

I wouldn't overthink elephant trunks too much, its a huge hole with a sock on it. In your case I would drill them as low as possible without messing up the fabric to transom attachments, or the floorboard to transom attachments. If that means its above your floor so be it. If a bit below your floor great. Just don't mess with the anything floor to transom attachment related area. I'd suggest a very short tube with a flange on the inside. Screw the flange to the inside of the transom with SS screws. A aluminum tube with flange could be made by a local welder, probably SS as well if you went that route. Band clamp your PVC trunk to the outside.

I'll try to put up some pictures of mine soon.
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Old 22 December 2011, 23:18   #10
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Captnjack, thank you That is the kind of information I was looking for. Please share a photo as the elephant trunk needs to be coordinated with my transom wheel project that is ready to be mounted, maybe even this weekend. Plus my transducer needs to find a new home somewhere on the starboard side where the transom wheels and future home of the elephant trunk aren't going to be located.

8: Where does the seam go? It seems like on the outside as in the second photo looks like the most appropriate. Also how much overlap? I was thinking somewhere around 3/4" = 19mm. Of course looking at the kit on rib-shop.com it appears to be glued round at the stern mount, then glued in two spots on the top part to force it to lay flat. The flat part could be sewn for strength, shown in the second photo. It will loose some water flow capability sewing it so it lays flat. For the fabric you suggest a 10 oz, how thick is that? I have some PVC for repairing my SIB that is .040 = 1mm thick. It seems stiff for this application as I do not think it would lie out flat enough to close off water flow back in. Although if sewn on the two sides and glued like the ones in the photos it might work?? It is heavy duty stuff, and actually thicker than my boat.





I like the idea of building a diameter towards the 3" size and only having one trunk. I still am not clear whether it should be above and partially below the deck or just above the deck for a hard decked SIB? My goal is to drain a fully flooded boat in a matter of seconds. I know for a fact the two below deck scuppers take about 10 minutes to drain a fully flooded boat. Learned after an unfortunate accident that took place on shore when a HUGE wake from a passing ship swamped it while on a beach. Fortunately it didn't do that much damage but did split a seam on the port speed tube from the added water weight and my battery sat underwater long enough to eat the positive battery bolt down some and it was stainless.

I have a tig welder and can make something like this below (They sell for $128 ), if I can find some scrap 3" OD tubing from our local salvage yard. I already have the plate metal required. Will need to buy the actual 3" hole saw, but I have a drill press, and the chuck for the hole saw. Stainless is a pain to drill, but easy enough to weld. Aluminum is easy to drill, but for me a pain to weld. Gonna drill the transom before the stainless plate, as no matter how slow I spin the hole saw it is going to tear it up. I like the idea of making a plug for it, but am not sure it really matters much "if" the hole is mounted above the deck height it can only allow so much water into the boat. I have had about 2+" of water just from leaving the lame factory scupper plugs out and leaving a set of doubles with my weight belt in the back of the boat. The water exits once back on plane.



These are more cost effective, but still winds up being almost as much as the entire trunk kit from the rib shop.
Primex Thru-Hull Fitting 3 Inch Fiberglass Exhaust Fittings

Anyone else have photos of their trunk setup, or comments to share?
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