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New boat. Rotten deck. DIY battle

27K views 261 replies 24 participants last post by  JimmusUK 
#1 · (Edited)
Hey,

I've recently bought my first boat (a 15 foot seahog style fishing boat) and whilst I was super thorough checking the engine and hull which are all in great condition, I've noticed the deck is spongy in spots.

After drilling pilot holes, there is basically nowhere on the deck that isn't either delaminated or has a thoroughly soaked ply base. The wood is places is soft, but not black pith.

The main stringer is rotten at the bow and wet throughout and probably not structurally sound.

I am going to tackle this job myself.

I have no boat repairing experience.

I have made two successful surfboards so have a little experience fiberglassing.

I don't have all the best tools but have quite a range of standard tools (drills, angle grinder, circular saws etc).

With that in mind, from those of you that are more experienced is there anything I absolutely must know before I start chopping the deck up?

What wood should I use for replacement stringer?

I do not have an electric sander so have ordered an attachment for my drill which I hope can suffice. When I made surfboards, I hand sander for ten plus hours, don't fancy that again.

I have ordered 450g cloth and a roll of strong neat topping cloth along with about 5kg of resin.

After cutting out patches of deck I can see the plywood is about 10mm thick, but will order 12 or 18mm ply to replace.

The deck is roughly 2.5 x 1.5m. A little more if I go right up into the cabin and right back to the stern.

If I am to cover that much wood in resin and then glass it, do you think I'll need another 5kg of resin?

Thanks in advance


Edit - lessons learned so far

  1. Don't buy an old boat unless you want to spend a lot of time fixing it lol
  2. When cutting out a deck try to cut as close to the edges/sides of the hull as possible
  3. When lifting a 40hp+ engine get Two people or an engine stand with wheels
  4. Marine ply is super expensive, have enough budget for this
  5. Loads more upcoming mistakes to learn from!
Threads that have helped me with tonnes of techniques and advice:

Tools used

  • Angle grinder for cutting up fiberglass and cutting off old rotten bolts
    • Thin cutting disk
    • Grinding disk
    • Have ordered a diamond etched tile cutting disc to see if that's better
    • Have ordered various sanding pads and discs in an effort not to buy a dedicated sander
  • Hammer, chisel and crowbar for pulling up old ply
  • Screwdrivers
  • Socket sets and torque wrench (13mm and 19mm sockets are gold dust for this boat)
  • Circular saw
  • Multitool was great for the 30 minutes it lasted before it broke and created way less dust
  • Spanners
  • Pliers
  • Drill obviously for drilling but have used to drill out rusted bolts too
    • Wire brush attachment to clean up metal and dig out old rotten wood
  • Wire cutters
  • Wd40 to loosen old bolts
Products (mentioned by members, or * used myself)
 

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#3 ·
To do the floor properly I would say you will need much more than 5 kg of resin. I've had 11 boats now and "rebuilt" at least 9 of them in the last 30/35 yrs. My last one is the one in my avitar. I put the whole "resto" on here with loads of pics, and quite a few others have done that too, have a look through the old posts. My one is in the link if you want to see.
https://www.worldseafishing.com/forums/threads/my-new-project-task-force-q18.22744401/
And good luck with yours, I shall be watching with interest.
If you have questions just ask, there's loads on here willing to give you advice :smile2::thumbsup:
 
#4 ·
This is really great, thanks. I will read through it tonight.

I have had another go at the boat and lifted the foam that was in there. It was sodden underneath.

I think that I will have to cut out the entire deck right to the bow and back to the transom, taking out the rear bench and weird wooden cupboard that's been built. There is not a single bit of dry wood. The only way to dry it out is going to be to have nothing but the hull.

The stringer is so rotten. Definitely going to figure out how to get that out but am worried that I'll pierce the hull so will need to be super careful.

Looking forward to how much stronger and more sturdy this will make the boat though.
 
#6 · (Edited)
OK thanks. I'll see what I can find.

I'm assuming normal DIY stores don't sell marine ply?

Would you avoid re-foaming between any replaced cross beams? There is alot of foam pumped under the old deck.

So how much resin would you recommend for a 15ft boat where most of the deck needs replacing and the ply coating before glassing?

What thickness of ply would you recommend?
 
#7 ·
OK thanks. I'll see what I can find.

I'm assuming normal DIY stores don't sell marine ply?

Would you avoid re-foaming between any replaced cross beams? There is alot of foam pumped under the old deck.

So how much resin would you recommend for a 15ft boat where most of the deck needs replacing and the ply coating before glassing?

What thickness of ply would you recommend?
I buy all mine from a independent timber yard, some of the big names like travis Perkins sell marine ply. Try look for an independent timber yard local to you

Personally I would rip out all the foam possible as it will just soak up water and trap inside making the boat very heavy!
Best bet is to leave open and put a bung in the stern if not already fitted.
Also make sure you leave holes/gaps in the cross members to allow water to drain back from all parts of the hull, this allows you to drain any water out should it get in the hull once sealed.
Ill have to get back to you on resin, trying to work out in my head!

I would go 12mm or 18mm depending on the span between supports
 
#8 ·
Nice thanks, really helpful. I'll order another 5kg and see how far the 10kg gets me.

Spare resin and glass is definitely not a problem as I want to build up over the current cabin as its only about chest high when standing on the deck which won't protect me or Fishfinder from the wind!
 
#11 ·
I have had another go at the boat and lifted the foam that was in there. It was sodden underneath.
I think that I will have to cut out the entire deck right to the bow and back to the transom, taking out the rear bench and weird wooden cupboard that's been built. There is not a single bit of dry wood. The only way to dry it out is going to be to have nothing but the hull.
This is exactly what I had, stripped the lot.
And you NEED, and I mean NEED to check the wood in the transom too, nearly all my boats I have had has had a rotten one.
Drill some plugs in it to get through the glass from top to bottom on the inside of the boat and in different places (not right through tho) to see what state the wood is like in the transom, I suspect you will find it's rotten as well as your floor is.
If it turns out the transom is ok you can "patch any holes" you make. This bit is very, very important.

The stringer is so rotten. Definitely going to figure out how to get that out but am worried that I'll pierce the hull so will need to be super careful.
A grinder and a steel cutting disc, goes through fibrglass "like a hot knife through butter", I use the 4" one

Make sure you go with marine ply when you replace and resin coat the underside before fitting. As for the supports, go for a hardwood beam. Most timber yards will have off cuts of oak or iroko
I agree with Matrndll, but I built the supports/strengtheners for the floor with 18mm marine ply and glassed them in place.

Would you avoid re-foaming between any replaced cross beams? There is alot of foam pumped under the old deck.
What thickness of ply would you recommend?
I would deffo get rid of the foam, and I filled the "gaps" under my floor with sealed milk bottles. Each one is an "air pocket" if you think about it, and they won't soak up water like foam will.
Can't remember what ply I put on my floor (think it was 9mm), but you need a fair bit of strength in the supports underneath to make it nice and ridged, and then plenty of glass. You don't need 18mm tho.

I want to build up over the current cabin as its only about chest high when standing on the deck which won't protect me or Fishfinder from the wind!
I done that on mine, got a walk in cuddy/cabin (but I think my boat is big enough to take it). It all depends on the size of the boat and the weight you will add "up top", as it could make your boat a bit "unstable". You will have to "mock" it up and see for yourself if it looks right, or will be right if you know what I mean. A lot don't like what I have done, they say it's too big, but I have to stand and drive the boat as I have a back problem and if I "sit n steer" i'll "suffer every wave" lol. And I don't worry about if someone don't like my boat Hahahaha.

you would have thought they would have done it in marine ply
gggrŕr
I think they probably did originally bud, it's just "the ravages of time" have got the better of an "old boat".

JimmusUK, please keep taking pics as you go and post them. I enjoy following these rebuilds and keep going, there's a fair job ahead of you but it will be worth it in the end as you will get great satisfaction from using something you "brought back to life" :):thumbsup::thumbsup:
 
#13 ·
This is exactly what I had, stripped the lot.
And you NEED, and I mean NEED to check the wood in the transom too, nearly all my boats I have had has had a rotten one.
Drill some plugs in it to get through the glass from top to bottom on the inside of the boat and in different places (not right through tho) to see what state the wood is like in the transom, I suspect you will find it's rotten as well as your floor is.
If it turns out the transom is ok you can "patch any holes" you make. This bit is very, very important.


A grinder and a steel cutting disc, goes through fibrglass "like a hot knife through butter", I use the 4" one


I agree with Matrndll, but I built the supports/strengtheners for the floor with 18mm marine ply and glassed them in place.


I would deffo get rid of the foam, and I filled the "gaps" under my floor with sealed milk bottles. Each one is an "air pocket" if you think about it, and they won't soak up water like foam will.
Can't remember what ply I put on my floor (think it was 9mm), but you need a fair bit of strength in the supports underneath to make it nice and ridged, and then plenty of glass. You don't need 18mm tho.


I done that on mine, got a walk in cuddy/cabin (but I think my boat is big enough to take it). It all depends on the size of the boat and the weight you will add "up top", as it could make your boat a bit "unstable". You will have to "mock" it up and see for yourself if it looks right, or will be right if you know what I mean. A lot don't like what I have done, they say it's too big, but I have to stand and drive the boat as I have a back problem and if I "sit n steer" i'll "suffer every wave" lol. And I don't worry about if someone don't like my boat Hahahaha.


I think they probably did originally bud, it's just "the ravages of time" have got the better of an "old boat".

JimmusUK, please keep taking pics as you go and post them. I enjoy following these rebuilds and keep going, there's a fair job ahead of you but it will be worth it in the end as you will get great satisfaction from using something you "brought back to life" :):thumbsup::thumbsup:
Thanks for all the advice. I'll go for perhaps 12mm ply then with more crossbeams as that's hugely more affordable than 18mm+.

The milk bottle idea is a good one, thanks.

You've scared me with the transom. I've got my head around the deck construction and am confident I can muddle through, but I've not researched how the transom joins to the rest of the boat (under the fiberglass I mean) and or the correct wood to use for that, how to disconnect the engine, whether I can even lift a 40hp on my own!

Is there a way to reinforce from the outside or would that be ineffective?

I am literally too scared right now drill a pilot hole. I don't want this to become an unfinished project, so the smaller I can keep it the better.

I really should give you all address to that you can knock on the door and chase up progress until its complete!

Can I get away with focusing on the deck, ensuring that's complete and solid and THEN investigate the transom or should this be all done as one job?

My focus today is to get that double glazing ripped out and the rest of the floor at the bow and stern cut out and lifted off. I'd love to clear all the wet wood out too if I have time.

I am hoping that I can work around the steering column and cabin as touching that will require me to strip all the electrics out which I'd like to avoid.
 
#14 ·
What are your thoughts on fibreboard

"Fiberboard is a popular alternative to marine plywood. Medium density fiberboard is particularly strong and has high durability. It is actually made in such a way that it is not 100 percent wood. To build up the strength of the wood, it contains a wax resin as well. When the wood is made, broken down fibers of softwood are mixed in with a wax resin. Ultimately, this creates a very strong end product. It is then cut into sheets and treated with extremely high heat and pressure. This makes the wood very durable and an ideal alternative to marine plywood."
 
#15 ·
Further progress and I've got a lot of the deck out. Can't believe how many worms and slugs were living under there.

Turns out the foam that had been injected in was blocking the water's route to the drainage hole which I've now cleared down.

There is a second layer of fiberglass up near the cabin which feels quite stiff but probably has rotten wood under it.

Do you think that I should try to take that out too? I am worried about going through the hull!!

I need an architect to help me with the cabin. I can't see how to make it useful. Ideally I'd like a little bench for the Toddlers to sit on out of the weather. Anyway, best not get ahead of myself.
 

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#16 ·
If you do the floor and the transom is rotten you will have to remove the rear part of the floor to get to the bottom part. Drill some test holes from the inside and only into the wood not all the way through. If the wood comes out dry and normal wood colour then seal the holes and carry on with the floor. If the wood comes out dark and or wet you will need to remove the old wood and replace. If you have to do it, cut the splash well out and remove the inner skin to get to the wood.
Do a search there have been a few on here.
 
#17 ·
OK. I'll do some research so that I understand the structure. I will wait until I've completely stripped the deck and worked out how I am going to make a stringer and floor joists.

I may even dry fit all the deck supports and stringer before I test the transom but I won't fit the deck until I'm sure the transom is dry.

I definitely don't have enough morale to take the engine off and cut more fiberglass out right now.

Will the hull be strong enough to stand in while I work? Wondering if I should get some boarding down when I'm back in there next time?
 
#22 ·
I'll check the transom

I've been reading about celotex ply topped ribs. Now this sounds much easier to work than solid wood ribs and light.

How would you feel about a full length celotex stringer front to back to replace the two to three part wet stringer that's in place?
 
#24 ·
I'll check the transom

I've been reading about celotex ply topped ribs. Now this sounds much easier to work than solid wood ribs and light.

How would you feel about a full length celotex stringer front to back to replace the two to three part wet stringer that's in place?
Thats how I did mine. If you go to a builders merchant they may allow you to get some from their skip. The celotex insulation are often delivered with celotex skids so their forklift can get the forks under them., these get usually thrown away. Sometimes 100x50mm some 100x100mm.
AFTER doing the transom. Please check yours before getting too involved in doing the floor.



This is mine removed. Plan the cuts to make the transom repair easier. When it comes to refitting it I used strips of 3mm fiberglass glued onto the underside of the seams, then ground the seams on the outside a few inches either side and glassed over them. Then use a colour flowcoat to paint over the join and sand back and polish, or paint it if your boat is painted.





The thing to note is the glass becomes the strength of the stringer the foam just gives it shape. All my stringers and ribs were given 2 to 4 layers over the whole rib/stringer and onto the hull. Then further layers were laminated up the sides and onto the hull. The central keel stringer was made in two layers the lower a 100mm square piece of foam fully laminated then the upper is 50mm foam with a ply top to screw the deck to. The holes over the small stringers are limber holes to allow any water to drain into the bilge via bungs in the bilge well. These were formed using pieces of old gutter that was laminated to the hull before adding the stringer. I did it this way so ensure the foam was protected from absorbing water.
The whole lot was then covered in flowcoat to water proof the fiberglass. The tops were sanded before laying the deck so aid adhesion. The 12 mm ply was given 1 layer of 450g chopped strand on the underside and after being glued and screwed down, 2 layers of 450g then a flowcoat layer with block paving sand added to make it non slip.

 
#27 ·
Thats how I did mine. If you go to a builders merchant they may allow you to get some from their skip. The celotex insulation are often delivered with celotex skids so their forklift can get the forks under them., these get usually thrown away. Sometimes 100x50mm some 100x100mm.
AFTER doing the transom. Please check yours before getting too involved in doing the floor.

View attachment 1264903

This is mine removed. Plan the cuts to make the transom repair easier. When it comes to refitting it I used strips of 3mm fiberglass glued onto the underside of the seams, then ground the seams on the outside a few inches either side and glassed over them. Then use a colour flowcoat to paint over the join and sand back and polish, or paint it if your boat is painted.

View attachment 1264893

View attachment 1264891

The thing to note is the glass becomes the strength of the stringer the foam just gives it shape. All my stringers and ribs were given 2 to 4 layers over the whole rib/stringer and onto the hull. Then further layers were laminated up the sides and onto the hull. The central keel stringer was made in two layers the lower a 100mm square piece of foam fully laminated then the upper is 50mm foam with a ply top to screw the deck to. The holes over the small stringers are limber holes to allow any water to drain into the bilge via bungs in the bilge well. These were formed using pieces of old gutter that was laminated to the hull before adding the stringer. I did it this way so ensure the foam was protected from absorbing water.
The whole lot was then covered in flowcoat to water proof the fiberglass. The tops were sanded before laying the deck so aid adhesion. The 12 mm ply was given 1 layer of 450g chopped strand on the underside and after being glued and screwed down, 2 layers of 450g then a flowcoat layer with block paving sand added to make it non slip.

View attachment 1264901

Great, thanks. I really appreciate the detail. Your job is super neat, I doubt I'll achieve anything that nice but so long as I can make it strong then I'm happy.

I will leave what I've done to dry out this week as work tends to be 10-12 hour days at the moment. Hoping to finishing cutting out the cabin and cutting out the edges around the deck that I've left (I was worried about getting too close to the hull with the angle grinder).

Once completely gutted, I'll drill the transom. Jesus, I hope its dry as it feels very strong with zero movement even when the engine is tilted but I'm not holding out much hope.

I've had a look at celotex for delivery but can't justify it right now and am obviously unable to reach out to builders merchants right now S everyone is furloughed.

If I can't find a cheap source online I will have to hold out for my local DIY store to open again but that gives the boat time to dry and me time to do further research.

I'm still unsure where exactly to cut to get the back splash well out. I just can't see how it's going to not look horrific. Hmmm.
 
#26 ·
... although unsure how to get the splash well out without creating some horrific seams in the finish on the top.
I would after removing the engine, cut the seam where the splash well meets the transom the bit below the engine, cut along the seam on the rear of the transom towards the side of the hull probably at the same height of the top of the transom where the engine mounts, and level with the lower edge of the gunnel.
 
#28 ·
Ah OK that's making sense now. I relied before reading this. Shame you can't put beading all over a boat as that always saves me when tiling bathrooms lol

Would you cut the corners off with the splash well either side of the well, where the cletes and rod holders etc are? So the back of the boat is totally open?
 
#30 ·
Draw a straight line following the lower edge of the inside edge of the gunnel all the way to the rear of the boat and use that as your cut line. Then across the rear at about the height of the engine mounting on the transom or if there is a join where the topside meets the hull use that and cut inside the well as previously advised.
 
#34 ·
When I did mine there wasn't a single bit of original wood left that was good, yours looks the same.
I would say do the transom first, then the keel strip second (that will butt up to the transom equating to strength), then the stringers ect (these will also butt up to the transom giving more strength), then the floor can be fitted on top.
That vid from JonD should help keep you on track, it's good.
 
#35 ·
When I did mine there wasn't a single bit of original wood left that was good, yours looks the same.
I would say do the transom first, then the keel strip second (that will butt up to the transom equating to strength), then the stringers ect (these will also butt up to the transom giving more strength), then the floor can be fitted on top.
That vid from JonD should help keep you on track, it's good.
You knew it was coming....

Confirmed WET TRANSOM.

From the pics of @Neill posted above it looks as though instead of running a full length keel front to back, you can butt each rib up against the next which short sections that form a keel once all glassed.

Is that the case or is there a full length keel hidden underneath?

Thanks
 
#36 · (Edited)
No No No No........The keel front to back should not be "put in in pieces", it needs to be put in in as long a piece as you can.
That's my opinion anyway.
Then once it's glassed in well, you go across the boat with your stringers (or whatever there called lol) cutting them "over" the keel if you know what I mean.
 
#37 ·
The main keel stringer I made from 100mm square kingspan foam.It was laminated with 4 layers of 450g chopped strand mat. The ribs were then added to give a flat floor. After these 50mm kingspan was added between the ribs and again laminated with 4 layers of 450g mat. The ribs got the same treatment. The smaller stringers are the originals as they were dry were covered with 2 layers of mat. As previously stated the foam adds little strength to the structure its the glass that gives the rigidity. By making it in this way I ended up with a stepped keel stringer which is very strong. Prior to fitting this the bottom of the hull flexed alot with the structure I built it now does not even with my 130kg on it
 
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