Cracked hull repair, RIB with 2 ft crack

[Rop]

Hi there, after quite a lot of reading here it's time for my first post. I would appriciate some advise from the experts here. I'm from the Netherlands, if you don't understand my post, let me know, it could be a language issue.

I own a older Osprey Sparrowhawk RIB, 17ft. with a 75HP Mariner 2-stroke outboard, both boat and outboard are from 1989, according to last owner. I used it for half a year probably.

Problem
During my last trip my hull cracked, an almost 2 foot crack, lengthways, along a sprayrail. I cut out a piece of the deck to reach the crack from the inside and have a look at the construction. As shown on the picture, the hull was foamed, allthough not very solid (that might have caused excessive movement in the hull with the crack as a result).

I added a sketch with the floor construction as it was, a plate (green) was glued into the hull on a sprayrail, the space between this plate and hull (orange) was foamed. On top of this plate, fibreglass with polyesther resin is used, overlapping with the hull (blue).

What i did so far
Because the crack went below my console, it was impossible to do proper preparations and repair without removing the console. So I used the angle grinder and cut out the complete floor, only a couple of feet near the bow remained. Removed the motor and console as well to have good acces to the boat.

Transom
I cut away a piece of fibreglass to check the transom, this is fine, no rotten wood. There are a couple of cracks though, as shown around the hole, see picture. Transom only went down to the floor level, not to the bottom of the hull.

To do

• Repair crack from inside
• Repair cracks around bottom transom
• Reinforce former connection between hull and deck (had to do a lot of grinding there)
• Reinforce hull, ad a couple of layers of fibreglass to reinforce the hull
• Build stringers, every 1.5-2 ft. from wood, laminated with fibreglass in the hull
• ad knees to transom, connecting to stringers. Transom vibrated quite a lot (to much)
• rebuild floor
• Flip boat and do some reparations on bottom
• Build up boat (console, motor etc.)

This is where i can use some advice, starting with first 2 bullets. My experience with fibreglass is almost zero... which kind of fabric to use? Are my plans OK or should I repair my boat different?

I have a lot of pictures, if i need to drop some, let me know.

Cheers,
Rob

[tunnels]

Hi
Strakes are the weak point and as the bottom of the hull flex's up and down the 3 corners of the strake are the weak points This also happens with just ordinary power boats ! Been there and had this and been drumming the importance of filling strakes from end to end and glassing over the top . this stops the flex taking place localized the bottom still needs to flex to give you a better slightly softer ride ! If you took you boat out for a run and watche what and how much movement there is in the bottom it would scare you r pants off . Never fit semi bulkheads that would go across the hull this is a reall bad thing to do !!. By almeans fit stringers longtitudinally But they have to not only strengthen but need to also flex as well so make then from foam and glass If you want a recipy for that let me now!
The floatation fom in the bottom is a really bad place to have floatation in any kind of hull as when it gets swamped the it want to float and a hull will turn turtle and go up side down .
Grind and get rid of any damaged glass Use a 2 layers of csm 450 matt , on top of that 2 layers of 800 gram double bias glass that will come from 100 mm outside the strake down into and up back onto the hull . Double bias can be bought with a layer of chopped strand stitched on it al ready 800 will better to use . After this has all gone hard you need to fill the strake level on top with a H80 grade foam nothing softer will do !!. This can be stuck in on a layer of wet glass Again wait till its hard and grind flat Then another 2 layers of the same double bias but 50mm wider than what is already showing from the layers that went down and into the strake . so that top layer will in efect Take away all and any flex from the Strake ! Double bias glass is really good for this kind of work as it is able to take flex and 100% of the glass is doing its job .
Always fill the strake from one end to the other, totally !!!
Its the first place to look on any power boat that has strakes look for stress cracks !!
Have made lots power boats and lots ribs over the years and this had always been a major problem for some manufactures .

The hull will be made from polyester resin so take the next step and do your repairs with Vinylester resin !!

When you done all the work inside then sand fill and paint the cracks that appear outside .

Dont fill the chamber with exspanding foam again !! Its a waste if time and money . Its soaks water and gets heavy over time and you will be wondering why you boats is getting sluggish and blaming the poor motor .!!

[Herman]

Can you post a more general picture from the top? Showing what is there, and what is not there?

For the rest, Tunnels is right. Create some longitudinal stringers, after reinforcing the strakes. Use vinylester or epoxy for the repair. Polyester is useless over here.

Extend the stringers to take the load of the transom. This will help the transom stabilise. We did the same on the "Mats" which is the smaller boat of Herman den Blijker. Keep an eye on the mounting points of the engine. They should not interfere with the stringers. If so, angle the last 50 cm of the stringer outward slightly. Also keep the draining of the cockpit in mind. Your transom is OK? 75 HP is not much, and should not affect the transom much. It might be an "eigen frequency" which you will tackle by adding the stringers.

I could not contact you. Can you drop me an email (hbrouwerjr at brandscomposiet dot nl)

[Rop]

Thanks Tunnel and Herman! Absolutely helpfull!
Sorry for my late response, had quite a busy week and didn't log in until this weekend.

I never heard of filling strakes, might be interesting!
If I don't place semi-bulkheads across, and no foam, what will keep the hull in place? Can I make it that rigid that I can keep it empty? How about supporting the floor where I (big guy) stand and walk?

Yes, a recipy for longitudinally stringers is more than welcome.

CSM, this kind of fabric was used as final layer (inside boat), but seemed to be sprayed ? on there. Double bias glass is new to me, is that simular to this type of fabric?

A friend is rebuilding a RIB and ordered some resin for me allready. Don't know which exactly, i think it's Polyester Resin. Why should I not use this kind of Resin?


@ Herman, I just shot a couple of pics from the top, hope this answers your question. I will drop an email, thanks!

[tunnels]

Hi
If you are a little worried about the ridgidity lay a 1 450 csm with a 1 800 gram double bias and 1 450 csm over the top. But make sure you double up join in the very bottom in the keel a foot wide full length of the hull even part way up the transom , But do this over the top of the filled strakes and take it right out to the place where you floor was fitted in the very outer strakes .
Make a really nice job and finish with a generous resin coat rolled over the top of everything to keep the water out of the glass strands ( osmosis can start on the inside ) makes it water proof and easy to keep clean .Make sure the floors are well and truely sealed as well on the underside and the edges so water is kept out !!. If the boat gets salt water in under it will never dry out as the salt continually draws moisture out of the air for ever more !!!! .

Looking at the photos it would be worth the effort of taking that piece ot of the fron as well and doing the joj 100% all the way through from front to back !!.

[Herman]

If I see correctly, the crack is where the inner floor joins the bottom. Then the crack probably has been caused by extreme flexing of the sides. Then reinforcing below the floor is not of any help, and the sides should be stiffened up (or the hull made from more flexible material, but that is out of the question here).

In that case I can imagine that a couple of heavily reinforced frames from left to right, and protruding above the floor, can take the load. This will stiffen the sides, but will be a pain when walking in the boat, and also hinder water flow to the back.

And about the fabric: Yes, that is the same, but there are cheaper places...

[Rop]

Herman, the crack is at the sprayrail closest to the bottom, in the last picture of the first post you can see it. Next weekend I will have some time to spend on the boat, because I work outside I hope the weather is with me...

@Tunnels, probably a good idea to take first part out as well, allthough I have al little doubt because that part was build extremely rigid and keeps the front of the boat stable.

I first have to repair the crack now, the hull is slowly turning instable and difficult to work on, some reinforcement before continuing is neccesary.

[pistnbroke]

The new polyester resin will not stick to the old ..hence epoxy or vinylester.

[tunnels]

Originally Posted by Rop

Herman, the crack is at the sprayrail closest to the bottom, in the last picture of the first post you can see it. Next weekend I will have some time to spend on the boat, because I work outside I hope the weather is with me...

@Tunnels, probably a good idea to take first part out as well, allthough I have al little doubt because that part was build extremely rigid and keeps the front of the boat stable.

I first have to repair the crack now, the hull is slowly turning instable and difficult to work on, some reinforcement before continuing is neccesary.

Glass the whole length of the strake . where you stop will end up the weak point and if you get a mysterious leak sometime it will track full length of a strake believe me Have seen quite a few over the years ! Crak at th back and leaking at the front after forcing its way the total length of a bendy strake . Took 15 years mind you on the old hull i had .

[Rop]

Thanks, i planned to leave the tubes in place and stop somewhere close to the tubes, next layer a bit further back and so on. Like in the graph.

Still thinking what's the best way to support the new floor.

Tunnels, can I have the recipe for longitudinal stringers or can you tell me where I can find one?

http://www.boatdesign.net/forums/att...1&d=1313614195