1980 17' Magnum 171 Rebuild

[cmperry56]

Hello all, This is my first major rebuild and I thought I would document my journey here. Pictured below is my 1980 Magnum 171 Tri-hull by Magtex. It is 17' long with a 1983 Evenrude 140HP. I inherited it from my dad when he passed away last year. We have used it a few times but the deck is like a sponge. I know he did some repair one time to the transom but I don't think he did anything to the deck. He took good care of his stuff but it sat outside and the cover eventually ripped and let water in. What I am starting with can be seen in the pics below.

 

[GT1000000]

Re: 1980 17' Magnum 171 Rebuild

Hi and welcome cm,
That is a very nice looking hull and should end up better than new when you get it all restored...
I would like to come aboard and watch, cheer and help if I can, on this journey...
Have Fun and Best Regards,
GT1M

 

[Woodonglass]

Re: 1980 17' Magnum 171 Rebuild

Welcome to iBoats!

I suspect, since it's a family Pass Down, you'll want to do her up right. To do so you'll need removed the deck and inspect the stringers to determine their viability. If they are wet and rotting then you'll need to replace them as well. If indeed the transom has been replaced and is still sound then you can do the stringers and deck with the cap on and this restoration will be straight forward. I can be a bit challenging getting under the helm and foredeck but we'll help you with all of that. First thing to do is to get her stripped down to nothing and then get the deck cut out so you can see what lies below.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

GT1, WOG, Thanks. I can use all the encouragement & help I can get. I KNOW the stringers and deck will need replacing. It is spongy
all over except right down the middle where the main stringer is. That seems solid but I will replace it anyway since I will have to
do the outer stringers and deck anyway. I have already done a lot of research here and have a pretty good idea of how I will proceed.
Of course there is always a couple of "gotcha's" in a project like this. We'll see.



My initial basic plan is:
1. Remove current livewell and patch hole in side of hull.

2. Replace the stringers (probably with 8 pound pourable foam).

3. Replace the open cell foam under the deck with closed cell 2 pound pourable foam.

4. Build pads (2 pieces of 3/4" ply) to mount the front seat posts so there won't be big holes in the floor.

5. It currently has one 12 gallon tank. I plan to add another 12 gallon so I will have a total of 24 gallons. There will be one
on each side. This should eliminate a lot of the slosh effect on tight turns.
6. Move the batteries so there is one on each side as well.
7. I plan to seperate the back-to-back seats and use them towards the back.
8. Build a casting platform in the back with the livewell under it in front of the splash well. I will probably incorporate about
6" - 8" of the splash well for the casting platform. I am hoping to be able to have a small bait well in front of the livewell
between the 2 back seats.
9. Rebuild the front deck to include more water resistant side hatches, a front anchor storage and possibly a built-in cooler.
10. I want to figure out something better for the trolling motor mount up on the bow. The one there "works" but I would like have
something that looks better and is more out of the way.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Progress Report:

Sunday afternoon I pulled the seats, batteries, fuel tank, livewell lid/cushion and everything else screwed to the deck. I also pulled the carpet out and the side panels and kick panels.





The following pics show under the dash with the kick panles removed.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

I know my dad did some repair to the transom but I wasn't involved so I don't know exactly what he did. In the pics below it looks like he replaced a portion of the transom. You can see the original inside skin including cut lines. It looks like he probably lifted the cap, cut the inner skin to remove the old transom, added new wood, put the old inner skin back and then used resin only to cover it all. I won't know for sure if the lower part of the transom was replaced or not until I do a couple of core samples down there. I suspect I will probably end up replacing the transom just to be sure. We'll see.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Day 2 Progress

I started cutting deck out Wednesday evening. After I made the first cuts I discovered the fiberglass on the top of the deck would come up in one piece. It had come completely loose from the plywood. As you can see from these 2 pics, the plywood is still wet.



But wait. It gets worse. When I pulled the aft piece of deck (1/2" plywood), there was more wood. The piece on the left is actually a piece of 1/4" plywood.


One of the first things I noticed is how thin the stringer is.


Bottom of plywood. The only resin on the deck was in the top layer of glass.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

On to the foam. As you can tell in pics below someone (I assume my dad) added more foam when they "repaired" the deck. All the dark areas are where the foam was still wet on top. The other areas were full of water just not wet on top.



This is what I found on the stringers. Nothing but CSM, very little resin and a rotted 1x4.



These are after I removed some of the foam. Look at how the outside stringer was sort of scabbed on. Also notice in the second pic how the center stringer looks like it was 2 pieces. After looking closer I found that it looks like the short porion of the center stringer was formed like a box from 1/2" plywood. The tall portion appears to be a solid board, 2x6, 2x8....

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Day 3 Progress

Well I removed almost all of the foam from the port side today.



This pic is the inside of the port stringer.


I noticed what look like it was part of the center stringer was loose so I pulled it out. It ran about 5' from the bilge toward the bow. It was an apparent attempt to build a center block out for water to flow back to the drain into the bilge. The only problem was that they didn't secure it to the hull so when they poured the foam it swelled under the edge and under this block.


I expected to find the starboard side to be like the port but when I pulled the fiberglass loose from the deck I found that it was much worse. The holes were pushed through with my finger!

 

[jigngrub]

Re: 1980 17' Magnum 171 Rebuild

Your boat is well fermented, if it was a wine it'd be worth a fortune.

Looks like you've got a good handle on what to do and how to do it and you're making good progress.

I'd go ahead and replace the transom and make it one solid piece again.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Day 4 Progress

As you can see in the pics below I did get a little bit done last night.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Well after some thought over the past few months and getting started with the demo work I have figured out what I think I am going to do about the stringers. I don't want any wood below the deck so I plan to use foam board for the forms for the stringers, bilge sides, etc. See pics below. The first is the center stringer and the second is the port & starboard stringers.




I think this will work but the height of the center stringer is about 9". Do I have enough layers of CSM & 1708? Should I use a different combination of CSM and fabric? Thoughts, Opinions?

 

[GT1000000]

Re: 1980 17' Magnum 171 Rebuild

I definitely don't know what the engineering side of it is, but I think you would need at least a couple more layers of 1708 to make up for the lost strength of the wood that won't be there and you may have to cover the foam forms with something like aluminum foil to keep the resin from eating into it...
You might be able to use epoxy, which is stronger and might not eat into the foam and maybe use some of the newer type of cloth like a Kevlar weave...
The other consideration is that you laminations will have to be bubble/void free since all of the strength will be coming from the resin soaked cloth...
Also, keep in mind the added cost...

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Progress Report Day 5 & 6

Well most of the water logged foam & wood is gone.




Beginning to look much better. However, any questions concerning rebuilding the transom have been answered. Take a look at the pic below. This is a view of the transom on the starboard side. The mulch that is still standing is the bilge. No fiberglass except the inside of the bilge area. The dark wood just below the old deck line is the transom wood. There was NO fiberglass on it at all.Not even a light coat of resin.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Today's Progress

As you can see I got a little more done today. The live well is mostly gone and the foam & wood around it is gone. The center stringer is gone. Taking out the live well was a bear. It was glassed to the floor and hull side very well. The walls were very thick, 3/8" to 1/2" in some places. It was all resin too. No glass of any kind except where it was tabbed in. It looked like it was molded and then set in place. Any way as you can tell in the pictures the center stringer was easy to pull out. The resin was so thin in places toward the aft of the boat that there were places where you could tell they didn't put hardly any resin. Just enough in to make it stiff. Up towards the bow, however, the resin was much thicker and will be harder to remove.




The pic below shows what was left of the center stringer up toward the bow.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

GT1M, Can the foam be sealed with some kind of paint or coating? It seems like aluminum foil would tear easy and you would still have the same problem.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Bump

 

[GT1000000]

Re: 1980 17' Magnum 171 Rebuild

GT1M, Can the foam be sealed with some kind of paint or coating? It seems like aluminum foil would tear easy and you would still have the same problem.

Ooops! Sorry, I missed this...thanks for bumping it...
The idea behind the aluminum foil is simply to act as a barrier between the resin and the foam, so that the chemicals in the resin don't "eat" the foam...
There really should be no reason for the foil to tear, since you should only be laying wet out layers of cloth on the form...
Also note that you need to seal any overlaps of the foil with some clear packing tape to prevent the fumes and the resin that may seep under the foil and deteriorate the foam...
The heat generated by the process of the resin curing also generates a significant amount of heat which could also melt or distort the foam...
The aluminum foil may or may not help with this also.
The denser the the foam the less this will be a problem...
In the past, I worked at a scenery production company where we made all kinds of "props" for TV and Videos...
We did use latex paint to paint foams, including plain old EPS [ extruded polystyrene, aka styrofoam] to seal them against the detrimental effects of the resins...also note that most of the resins we used are the same ones most boats are built out of, polyester resin, not epoxies...
Sometimes we even used expanding urethane foams to make molds and then cover them with fiberglass, it was an expensive and time consuming way to do it, but the biggest advantage was being able to make complex shapes and not having to worry about the resin eating into it...
In most cases, if the foam was thoroughly and properly sealed, after the first layer of resin soaked cloth was applied, there would be very little or no distortion/melting of the underlying foam...
Afterwards, any subsequent layers would have no effect on the original foam form...
In some cases we even went back and removed the foam form because, for whatever reason, the final shape needed to be hollow...for those times we would spray PVA on or mold parting wax, to the completely foil wrapped form before applying the resin...
There are special foams available that can withstand direct applications of resin, you just need to search for them...
There are also special core products, like "Nidacore" and their equivalents that can be used the way you want...the caveat is that 3M, the owner of "Nidacore" has decided to cease all production of these products, so you will have to look for NOS wherever it may be, or look for a different manufacturer of these products...
Hope this helps and great looking progress on the demo, so far...Keep up the great work!

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Progress Update

Nearly all of the water logged foam and wood is gone. There is a little bit left under the cap between the 2 consoles. Will work on that tomorrow. I also plan to build a couple of braces to brace up under the hull just in front of the windshields. Before I do that I plan to take it out of the garage and rinse the dust off.





These 2 pics are under the consoles.

 

[cmperry56]

Re: 1980 17' Magnum 171 Rebuild

Hey, does anyone know of a good thread to look at where they cut off the splash well section of the cap to do a transom rebuild and then put it back? I am considering doing that on this one because I don't have any place to set the entire cap while I do transom, deck & stringers. As you can see from some of the pics, I am doing this in my garage.