Stuck Sponsons on Tubes

[ThomasMoroney]

So my 90 mongoose has stuck sponsons. Sort of a restoration build for this season… I would like to pull them off INTACT! Assess their integrity and possible solutions, and go from there.


The issue is:

-The brass sponson tubes have become misshapen. They have split and have become swollen in spots.

-The aluminum boom tubes were oxidized which could have caused the swelling and bursting. Possible that trapped water froze due to poor winter storage.

-I fear that the oxidation bond is stronger than the epoxy holding the brass tubes in! I did not build this hull, nor do I know its structure.


Attempts at resolving the issue. Nothing below has budged the tubes.

-I tried using a floor jack, gently.

-I have tried a pair of spreaders.

-Tapping lightly with a rubber mallet.

-Using penetrating oil

 

[Mike Hughes]

With the way they are bent, you going have a tough time trying to reuse these. With that being said. I think your best bet to cut them off an drill them out. Even if you have to make the hole a little bigger. You can rerig the tub on a set up board and glue the new tubes in. That way your angles are all correct. That is how I normally fix my carbon ones.

Mike

 

[Brian Sorgente]

Lightly clamp the sponson to your work bench and heat the END of the brass tube with a heat gun or torch on low while gently pulling and twisting the tube with your other hand. When the brass tube heats up enough inside the sponson, the epoxy holding it in will let go and the tube will slip right out. Go slow, it wont take long.

Brian

 

[ThomasMoroney]

I should have made it more clear, the aluminum boom tubes are still attached to the hull, and of course cannot come out.

-Mike, do you have any pictures of your setup board or a past repair? This hull is my first foray into the hobby. I also do not have much info as to the angles and such for setup.

-Brian, the sponsons are still attached to the hull. Sorry the pictures do not show that. There will be no twisting. As far as heat goes, how will the foam cores respond to that? I have used heat to separate epoxy before. If it smokes you torched it too long... But never had foam in the mix.

A fix I thought of is to chop em off flush to the sponson. Pull/drill (how would I drill it by hand?) out the brass from sponson, replace with a carbon tube which will slide over aluminum boom and bolt near the hull. I just do not know if that would be rigid enough. Does anyone know how long the aluminum boom inserts into the brass? How are the mongoose sponsons built as far as the brass tube is concerned?

 

[PaulHail]

Consider the booms scrap, so cut them off with a hacksaw, then use the heat and twist as mentioned. Epoxy starts to get soft around 180F, foam melts a bit over 400F depending on what type of foam. If a little bit of the foam comes out stuck to the brass tube, just use some filler with the epoxy when you glue in a replacement tube.

My SWAG would be galvanic corrosion is what caused your problem.

Aircraft spruce and specialty has reasonable prices on aluminum tubing for replacement booms.

 

[Brian Sorgente]

I agree with Paul. You can also go with carbon/ fiberglass booms which will not corrode. They offer several different types at Goodwinds.com and they are made to tight tolerances so you can basically pick whatever size you need and still have a nice tight fit inside the new brass tube.

Brian

 

[Ray Sametz]

Consider the booms scrap, so cut them off with a hacksaw, then use the heat and twist as mentioned. Epoxy starts to get soft around 180F, foam melts a bit over 400F depending on what type of foam. If a little bit of the foam comes out stuck to the brass tube, just use some filler with the epoxy when you glue in a replacement tube.

My SWAG would be galvanic corrosion is what caused your problem.

Aircraft spruce and specialty has reasonable prices on aluminum tubing for replacement booms.

I agree with Paul. You can also go with carbon/ fiberglass booms which will not corrode. They offer several different types at Goodwinds.com and they are made to tight tolerances so you can basically pick whatever size you need and still have a nice tight fit inside the new brass tube.

Brian

I agree, the booms are scrap. Try the heat method, but first PM Andy Brown he built the boats see what he says.

 

[bermudadude]

take more visual pics of the whole boat and post ,then see if you can get Andy Brown to chime in. i personally didnt realize the brass tube went deep into the sponson and tore up one a decade ago trying to get it off. i BELIEVE heat was involved to get the other one off . cut em off close to the tub and use heat and twisting like mentioned and the whole alu tube with brass sheath should come out. trash the metal then source the right size brass to glue back in and use alu again or like someone said source the carbon. that heavy boat would benefit from carbon tubes.

only going off my experience. andys boats where ,and are,constanty evolving so the inside of ur sponson may not be the same but if its old enough its the standard white foam with hardwood blocks holding the tubes so u have to keep the heat on the tube but away from the sponson. good luck

 

[Mike Hughes]

-Mike, do you have any pictures of your setup board or a past repair? This hull is my first foray into the hobby. I also do not have much info as to the angles and such for setup.

Click on my photo album link below. Lots of pics of a twin and X hydro repairs in there. Any nice flat surface will work for a setup board. I use my work bench top all the time. Take your turn fin/rudder off. Set boat on top. Take measurements of it before you go cutting it up.

Mike

 

[Andy Brown]

If the booms are not bent I would leave everything intact and go with it.

Fill the cracked brass and paint with the sponsons for better looks.

The sponsons are white polystyrene with large wood dowels to support the tubes.

All is assembled with 5 min. epoxy.

If you MUST remove the sponsons, use Brian Sorgente's method of heating. After that the brass will have

to be "pealed" and sanded off the boom.

The booms are solid and to "update" with lighter tubes would ruin the performance of the boat

unless you want to see it fly off the water at 55 mph.

The front boom is pinned in place to a birch bulkhead with alloy 6-32 screws.

So it's not coming out without some serious rebuild.

Yes it is a heavy old boat, but the 90 Mongoose dominated the race course in the late 1980's

and set the IMPBA F hydro SAW record with a CMB 90 GP. in 1988 @ 80+ mph. Huntsville lake, complete with ski jump and ski buoys.

Would be great if you could post more pics of the complete boat Thomas.

 

[ThomasMoroney]

Thanks again for replying Andy!

This is how she sits currently. This hull was given to me to be a quick get in the water boat. Unfortunately it needs a little tlc in every corner and I have committed to much already, even though it does not look it... It was formally painted in a Frosted Flakes scheme. It has since been stripped, since I do not have the cowl, I figured I would start it fresh. I do not have access to the one and only pic i have prior to stripping at this moment. I will get a thread going as she comes together, highlighting some of the rebuild. Which reminds me, does the blog feature not work on this site? That seems like a good place to highlight projects without adding threads.

 

[PaulHail]

One thing I've learned about brass from reloading is that when it becomes discolored and cracked, it is most likely very brittle as well. So if you can replace the brass w/o damaging the sponsons IMHO it would be worth the effort.

 

[ThomasMoroney]

My next thought is what would happen to the aluminum during the heating? I know epoxy lets go at low temps, but doesn't aluminum's integrity diminish with excess heat? I would only attempt to do this with plans of saving the aluminum tubes in their entirety. It may take extra heat on the exposed brass to get the epoxy to let go at the farther point in the sponson. Paul that is good to know. One more mental notch on the "repair it" side! I cannot get this issue off my mind. Every night it calls to me...

 

[PaulHail]

Aluminum is somewhat complex in annealing in that it anneals around 775F, depending on the alloy, and it age hardens at 350F, again depending on the alloy. As mentioned previously, epoxy gets pretty soft at 180F, though it will start softening at 140F. While foam melts at about 400F, it starts getting soft at 212F.

Probably you're safest route is to heat the aluminum tube with a heat gun so you don't get it too hot and keep tugging on the sponson until the brass tubes let loose.

If it was me I'd just cut the booms and order replacement aluminum tubing or round stock from Aircraft Spruce or whoever you can get the best price from. Likely under $20 for the material for new booms.

 

[Ray Sametz]

My next thought is what would happen to the aluminum during the heating? I know epoxy lets go at low temps, but doesn't aluminum's integrity diminish with excess heat? I would only attempt to do this with plans of saving the aluminum tubes in their entirety. It may take extra heat on the exposed brass to get the epoxy to let go at the farther point in the sponson. Paul that is good to know. One more mental notch on the "repair it" side! I cannot get this issue off my mind. Every night it calls to me...

I see maybe a road trip in your future. Since your new at this, stop by the shop. Pm me a phone #.

 

[happybradboating]

Hello, I think what I would do is mask off the sponson rods with tape and paper. Then paint the hull as you see fit. I would say that is better than having to worry about damaging your sponson(s). I have personally ruined enough sponson's trying to get everything apart. If it is not wrecked leave the sponsons alone. If needed mask off the whole hull separately and spray the sponson's. Then reverse the process for the other part of the boat, i.e. hull. Just an afterthought!

 

[ThomasMoroney]

Yes that is true!

I did however just have an aha moment that allows the tubes to twist without harming the front aluminum rod, in theory. Since the back aluminum rod is easily replaced, because its bolted in and accessible, you cut that one. It is easily replaced with a new one. This allows the sponson to spin with less heat needed then the straight pull method.

 

[Brian Sorgente]

Ohhh now that I see why you wouldn't want to remove the booms, or the front one anyway. I didn't realize I was built into the tub... Yes, if you cut the rear boom then you can twist the sponson and pull while you heat so you can salvage the front one. Might be good to have another person hold the aluminum tube with some plyers at the same time so you don't twist the boom loose from the front of the tub accidentally. Just wrap the aluminum with some scrap brass so you don't dig into it with the plyers.

When you get the sponson off, if you have trouble getting the brass tube off the aluminum you can use a cut off wheel on a dremel to slowly cut a notch down the length of the brass tube that was in the sponson. Cut little by little and when its VERY thin, take a flat head screwdriver and twist it in the slot. This should break it free so it will come off the aluminum tube without cutting into it.

Good luck and let us know how it turns out!

Brian

 

[Andy Brown]

I have been through all of this more than once. We build hundreds of those boats and I fixed several of them.

My final best advice - Fix the transom, paint it and go!

You won't even have to install the sponson/boom screws. Those sponsons will never move!

 

[ThomasMoroney]

Andy, you described the brass tube as held in by large dowels. I assume they have a near same od to the aluminum rods. How are the dowels built into the sponson? I need the picture painted in my head before I rationalize a restoration attempt, or I heed the safe play advice. Thanks!