Inflatable can you fit a self emptying trunk

[d1ve1n]

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

[C2 RIBS]

Originally Posted by d1ve1n

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

[jyasaki]

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

[Max...]

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.

[Nick Hearne]

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!!!

[Peter_C]

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?

[Max...]

Peter - try a search for 'elephants trunk' on here - loads of previous how to fit topics etc.

[Peter_C]

Originally Posted by Max...

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?

[captnjack]

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.

[Peter_C]

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?

[captnjack]

I glued up my tube from one piece of PVC, no sewing at all just a 1cm overlap and glued. 10oz fabric is pretty light and flexible about like a raincoat. 1mm sounds really thick and stiff.

I think you might be over estimating the ability of elephant trunks to actually do their job. Nothing except a boat with no transom at all will empty "within seconds."

If you stuff the bow once the most important thing you can do is reduce speed and/or change course immediately. Any boat 1/3rd full of water is riding low so you're highly likely to stuff the bow again. The second wave will carry in ALOT more water and swamp the boat to the gunnels. No matter what its going to take a few minutes to get back to normal, depending on speed, bow rise and if any more water is coming aboard.

[Northern Pike]

Originally Posted by Peter_C

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.

Stainless is a pain to drill, but easy enough to weld. Aluminum is easy to drill, but for me a pain to weld.

I'm interested to see what you come up with. There's not much room on the transom for all that. I've been having a hard time finding a suitable location to mount my transducer. Sounds like our boats are similar, so please keep us posted.
Remember when drilling stainless, low speed, high feed, and lots of oil. No problem.
Good luck, and Merry Christmas!

[Peter_C]

Originally Posted by Northern Pike

I'm interested to see what you come up with. There's not much room on the transom for all that. I've been having a hard time finding a suitable location to mount my transducer. Sounds like our boats are similar, so please keep us posted.
Remember when drilling stainless, low speed, high feed, and lots of oil. No problem.
Good luck, and Merry Christmas!

Don't forget the trailer bunks getting in the way too! You do not ever want to have anything you have to remember to pull or move before putting the boat on the trailer. It can be an expensive mistake when you or someone else trashes a transducer. I have seen it before. All my boats have been setup to pull right up on their trailers, even with fenders in place.

I found this at HF and other places. Might just be the ticket assuming it goes over a 3" stainless pipe I still need to locate first.



3" x 25 Ft. PVC Discharge Hose

You can buy it here by the foot.
PVC Lay Flat Discharge Hose 3" - FarmTek

[m chappelow]

Hi peter-c
the boat in the photos is mine and dont worry about using the photo,s thats what they were put on this site for in the first place ,glad they could be of use ,

i used to have a Humber 16 ft heavy duty work boat SiB and that only had a single 3inch diamiter drain trunk and it coped well with any water that came aboard ,, it was only glued into the hole on the wood transom and did not have any other fittings unlike the y boat in the pics which has fittings like cptn jacks ,,and was made from a tube of hypalon materiel,,
in all the years i had it it never started to come loose.

as a matter of intrest the y boat trunk holes are 3" 1/2 inches in diameter,,
reason that its a bit over kill on an 11 ft boat is that its a standard fitting on the next size up boat the RNLI use the ,,D class at 16 ft ,,as there are more d class boats than y boats it makes sense to use the availble fittings when building them,

you may have seen it before but this clip shows example of one of the d class boats being launched and how fast the trunks work .

www.youtube.com/watch?v=n4OcLgBYjzs

[jyasaki]

Pete;

I think you're overthinking things (and possibly, oversizing.)

The drain is only going to work while moving forward (unless your boat is on the trailer.) having it seal up (mostly) by collapsing isn't that big a deal; you simply drop them just prior to hitting the throttle, and pull them up before stopping (if you're worried about swell or wakes), or just after you've drained the water (in a non-recurring type of event.)

Not sure you really need to go three inches, but if you have the room on the transom, bigger is probably better. My boat (which you've seen) is running two 1.5" trunks to drain the deck (bilge is by electric pump.) I doubt you're going to get a solid 3" stream of water exiting the boat anytime you're in the water: if totally swamped, you'll have problems getting the trunk high enough to clear the waterline; if you have a small enough amount of water in the boat to plane up, you won't have enough water to span the trunk diameter.

If you want to go some other size (meaning I think your PVC drain tube material is fine), simply glue up a piece of PVC or hypalon in the appropriate diameter and stick it on. Hose clamp around, glue to the tube, or any other waterproof method will work fine. The tube mount will be clear of the water while underway. Flow through the tube will not be an issue, so seam restriction won't matter. No substantial strength needed, so I wouldn't worry about stitching it (the most stress it gets is from directing non-pressurized water out the back; sort of like the stress a garden hose is under while funneling water from a pitcher through it.)

As far as your 3" stainless tube, OnlineMetals.com has 304 welded tube in 3" OD for about $25/ft, or seamless for a few bucks more (thinwall; thickwall gets expensive pretty quickly.) They have other sizes if desired.

Weld a flange (or partial flange, if flush-to bottom) to the tube, cut tube to about 2 to 3" longer than the transom thickness, drill and seal the transom, slide through from inside, bolt or screw it in (seal all holes thoroughly), attach whatever trunk material, rig up a line to retract, secure, and deploy, and you're good to go.

See you in Monterey sometime;

jky

[captnjack]

The end doesn't need to be above the waterline.
If you're empty the tunk will work without moving forward.
If you have a heavy load it won't work very well unless you're moving forward.

Agree about not overthinking it too much, just cut a hole and attach tube.

[d1ve1n]

many thanks to you all for replying
i think i will have a go with the 68 mm kit that Ian suggests in the first reply
gary

[captnjack]

Originally Posted by d1ve1n

many thanks to you all for replying
i think i will have a go with the 68 mm kit that Ian suggests in the first reply
gary

Did you get yours fitted?
Here's mine
http://www.rib.net/forum/members/4333-albums201.html

[Peter_C]

cptnjack, nice boat! What did you wind up making the actual elephant trunk from? Do you know the thickness? From my internet arm chair it looks like very stiff material. I wonder if slicing the ends would help it flatten out to seal from water intrusion? Sewing the last couple inches of material definitely would flatten it out.

I bought enough stainless 316 3" tubing to make two elephant trunks although I am only going to use one. Happened to be a pre-cut piece the dealer had around. Even still expensive stuff at $25 cash. I then went to a farm supply and bought a few feet of 3" discharge hose as I posted above. I am not happy with it though as it seems too stiff. Looks kinda like what you have, but it is blue. The pvc tubing fits the stainless tubing pretty well and could easily be clamped up with some sealer between. Not sure which material I am going to use for the trunk yet.