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drew.ward · 04-05-2008, 12:00

Hey guys,

I am trying to determine if it's feasible to raise part of my deck on my ferro-cement boat. The aft cabin is really shallow and since I'm doing a full rebuild I was thinking I would cut off the top of the deck abaft of the cockpit and raise it up about 6-8 inches.

I have to do repairs back there anyway from some hurricane damage. Also the builder put quite a large amount of port space in the stern. I am going to rip out the homemade 'windows' he used and install something nicer.

So my thought was to fabricate some steel bracing that I could mount inside the boat to keep everything rigid. Then basically cut off the deck in this area. Then fabricate some permanent steel to act as a frame, tie back in with the existing hull and add new cement on top using plywood as a form.

The boat is in the water right now, and I was trying to decide if I should leave it in the water. I should still have room to do all the work, and my thinking is that the hull would have a truer shape with the water pressing on it than it would have in the boatyard. I know ferro isn't supposed to flex, but everything flexes some.

Does this sound like a disaster waiting to happen or a logical approach?

ssullivan · 04-05-2008, 12:45

The general premise is sound. I don't see anything wrong with the approach, so long as you make sure to use stainless steel for any structural member - or - paint that steel when needed like someone who has a steel boat would.

I can't speak to the joint between the old ferro and new ferro you plan to join. Someone with ferro expertise will have to do that. All other ideas are right on...

Quote:

Originally Posted by drew.ward

Hey guys,

I am trying to determine if it's feasible to raise part of my deck on my ferro-cement boat. The aft cabin is really shallow and since I'm doing a full rebuild I was thinking I would cut off the top of the deck abaft of the cockpit and raise it up about 6-8 inches.

I have to do repairs back there anyway from some hurricane damage. Also the builder put quite a large amount of port space in the stern. I am going to rip out the homemade 'windows' he used and install something nicer.

So my thought was to fabricate some steel bracing that I could mount inside the boat to keep everything rigid. Then basically cut off the deck in this area. Then fabricate some permanent steel to act as a frame, tie back in with the existing hull and add new cement on top using plywood as a form.

The boat is in the water right now, and I was trying to decide if I should leave it in the water. I should still have room to do all the work, and my thinking is that the hull would have a truer shape with the water pressing on it than it would have in the boatyard. I know ferro isn't supposed to flex, but everything flexes some.

Does this sound like a disaster waiting to happen or a logical approach?

Jolly Roger · 04-05-2008, 14:29

I owned a ferro ketch for seven years and did repairs, some under water, but nothing as big as this job.
What you would basically do is cut the hull with a cement saw all round about 6" down from the current deck level to the depth of the wire reinforcing, and the same on the inside. Then knock away the cement to expose the mesh – a hard messy job, easier said than done! Then build a new grid to the level you want by welding it to the old mesh. Then plaster it with the correct type of ferro cement and bonding chemical, fairing it in to the hull lines.
Having seen ferro hulls being plastered it is a very skilled job, by two men working fast inside and out, and I would have the plastering done by ferro experts.

**Hud3** · 04-05-2008, 14:38

Take a look at the yachtrodney thread. This intrepid gentleman cut his ferro in half to move it to a launch site, and then reassembled it in the water!

http://www.cruisersforum.com/forums/f9/yachtrodney-launched-last-after-15-years-11518.html

hooked on water · 04-05-2008, 16:03

I am with jolly roger, this is going to be a very big job and very hard
to lift the cabin top is going to need a good jacking system due to its weight
and you need to ensure that this does not compromise the design by checking with the original designer
and in the water spells alot of more difficult times when you need to be outside to align things
good luck
hooked

Gene :^) · 04-05-2008, 17:36

Would it be easier to just lower the floor in the aft cabin?

**Alan Wheeler** · 04-05-2008, 22:44

If I have this right, you are lifting a solid FC deck. This will raise the CG but I doubt 8" will be that detrimental. I assume you wanting to do this is so you can keep the Aft deck as is. Because one other choice is to build a new deck from timber and glass it. It helps reduce the weight up above the waterline.
Otherwise, I see no issues with what you have described. Either in or out of the water is fine. Support where you think you should. The job is messy and hard work, but quite possible. And if you take a look at YachtRodney, you will see that nothing is impossible.

drew.ward · 05-05-2008, 00:27

Thanks all around guys.

Yeah I don't really have any reason to raise the rest of the deck, it's in good shape and there is good headroom below. For some reason the hull shape gives the far aft area a really shallow layout. So this is only going to be adding 8 or so inches to the back 10-15 feet of the boat.

But that extra room on the inside is going to make the boat way more liveable overall -- especially galley wise.

cooper · 05-05-2008, 02:42

As above but remember ferro does flex. This is a good thing. I have had the flex thing proven to me in the most dramatic way by the designer/builder of my boat. As I have said many times before my hull is 3/8 inch thick. Imagine a piece roughly half a meter wide curved upwards in the middle about 100 mm (cant be exact but it dosnt matter in the point I am making) Place this hull section on the ground and stand on it. Now start gently at first bouncing up and down, (theatre convinces people !) till finally the whole piece is being completely flattened to the ground. This piece was cut out of a hull section from a similar boat to mine and used by Kan Walker to demonstrate ferros properties for years. Do make sure that the connection between hull and deck are sound. The chipping of the"concrete" to expose the armeture is the way to go. Then knitting that back into the new section. Be carefull of the "concrete"to "concrete" bond if adding new "concrete" This is the whole reason for plastering up in one go.

Messy yes but potentially a lot easier than any other boat building material.
( i havnt owned or worked on an Aluminium boat yet ; ) )

hooked on water · 05-05-2008, 22:13

wow that flex demo sounds really profound
wish I could see it
did not think there would be that much flex in it
a truly scary thought, aswell as confidence building in the boats we own
thanks for that info cooper
hooked

**Alan Wheeler** · 06-05-2008, 00:19

A bonding agent is needed and that is simply PVA. You can buy it as a real McCoy concrete bonding agent for four times the money or as plain old PVA.

cooper · 06-05-2008, 02:35

A preferable method of bonding is using an amine cured epoxy, directly coated on the existing concrete and while still uncured, the new section is added. As an example see.

http://www.megapoxy.com/downloads/H_TB.pdf
see section 5.

There are many brands that are suitable.

ps . the display of flex amazed me too. Since then I have met up with a number of other Kan walker ferro boat owners and their hulls are of a similar thickness. The down side (and I am a realist) is that ferro can suffer from "localized impact" In simple terms ferro dosnt like sharp pointy objects belted against it. Usually the surface strike area can result in a four times larger break out on the inside. The plus is emergency repairs are easy. One decent tub of "under water concrete" and the problem is fixed.
Try fiber glassing underwater.....or welding or.....

**GordMay** · 06-05-2008, 02:44

What is “plain old” Polyvinyl Acetate (PVA)?

cooper · 06-05-2008, 02:49

..same thing as "bondcrette" sold here in Aus and NZ. PVA is sold as everything from craft glue to timber glue . Some of the newer formulations are a lot more job specific, but back in the old days.......