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Old 03-26-2023, 06:49 AM   #21
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Just curious, are there any negatives to having a forever damp/wet zone between the concrete and the FRP hull?
Not that I could see. In the pics you can see on each side I went to the fiberglass hull in an area. Under the concrete looked like brand new fiberglass.
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Old 03-26-2023, 08:08 AM   #22
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I'd think the biggest concern would be having enough water anywhere in there to cause freeze expansion damage during winter storage. As long as that's not an issue I wouldn't be worried.
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Old 03-26-2023, 08:14 AM   #23
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I'd think the biggest concern would be having enough water anywhere in there to cause freeze expansion damage during winter storage. As long as that's not an issue I wouldn't be worried.
I believe that is what caused this issue. Also had the same type of issue in the bilge floor, that I already repaired and took the opportunity to form a small sump lower for my bilge pumps to sit in.
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Old 03-26-2023, 10:28 AM   #24
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Hi Charlie
I painted my concrete under the aft cabin with 2 coats of Kilz rather than glass over. Something to think about, wont trap water…

Alan & Darina
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Old 03-26-2023, 10:41 AM   #25
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Are there any of them left?
Hah! Good question. There certainly must be, but I have to admit it's been a loooong time since I've noticed any ferrocement yachts, anywhere.
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Old 03-26-2023, 11:17 AM   #26
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Greetings,
Mr. s. Re: Your post #20 regarding "...forever damp/wet zone...". Other than the freeze/thaw cycle Mr. rs mentioned, one, albeit remote, possibility is the growth of mildew/microbes which may reach a biomass sufficient to break the fiberglass layer(s) thus spreading toxins throughout the vessel. Just sayin'....


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Old 03-26-2023, 03:48 PM   #27
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Every ferrocement boat owner.
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Are there any of them left?
I can see one from my dock. About 60' ferrocement, give or take. Not a bad looking boat, but I've never seen it move.
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Old 03-26-2023, 04:18 PM   #28
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I can see one from my dock. About 60' ferrocement, give or take. Not a bad looking boat, but I've never seen it move.
Maybe afraid to move it???
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Old 03-28-2023, 07:34 AM   #29
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As opposed to the water on the outside? LOL
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Old 03-31-2023, 03:03 PM   #30
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Who would ever imagine having to do concrete work on your boat…

Fintry and all of her sisters have concrete in various places for trimming ballast. When we put in new freshwater tanks, we had to jackhammer out concrete -- about 20,000 pounds of it. The guys doing the work quickly got tired of carrying it ten feet up to the main deck and then down 20 feet to the deck of the railway, so they torched a hole in the side. That's one good thing (among other good things and some bad) about steel -- if you need to move something in or out, just cut a hole.


The bow compartment was a water ballast tank. We put the bow thruster there, so she now has lead encased in concrete to provide the weight to keep the bow down.


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Old 03-31-2023, 03:11 PM   #31
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I watched a video of a CG icebreaker getting a new engine. They cut a huge hole in the side and used some I beams to make a slide. Then they used hydraulic cylinders to push the side back in place when they were done. Pretty neat.
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Old 04-03-2023, 08:20 AM   #32
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Hi,

stupid question, why used concrete before?

NBs
Not stupid. I have heard of many trawlers putting 5-600 lbs in lazzarette. I assume this is for trim bit always wondered why none of the boat builders, or architects took this into consideration or changed the design. My 1973 GB36 had sand bags there. I took them out for a bunch of work and I am will probably leave them out to see what it does. I would love to hear all thoughts.
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Old 04-03-2023, 09:10 AM   #33
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When you are designing a boat, it is hard to get the F&A trim exactly right, particularly if there are various engine, tank, and battery options. That's true even now, with good computer design tools. In pre-computer days, getting trim even roughly right was a long mathematical exercise, listing the position of the center of gravity of everything on the boat in all three dimensions and the weight.


Sailboat designers can deal with this by adjusting the shape of the lead keel, but even then, many sailboats have some trimming ballast. Powerboat designers can move the engine(s), batteries and tanks F&A, but those options are limited and there's no ballast keel, so inside ballast is often needed. Concrete is cheaper than lead and has the advantage that it stays in one place. Lead needs to be held in place.


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Old 04-03-2023, 09:58 AM   #34
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When you are designing a boat, it is hard to get the F&A trim exactly right, particularly if there are various engine, tank, and battery options. That's true even now, with good computer design tools. In pre-computer days, getting trim even roughly right was a long mathematical exercise, listing the position of the center of gravity of everything on the boat in all three dimensions and the weight.


Sailboat designers can deal with this by adjusting the shape of the lead keel, but even then, many sailboats have some trimming ballast. Powerboat designers can move the engine(s), batteries and tanks F&A, but those options are limited and there's no ballast keel, so inside ballast is often needed. Concrete is cheaper than lead and has the advantage that it stays in one place. Lead needs to be held in place.


Jim
Thanks for the explanation. Full disclosure, this is my first powerboat transitioning from many years sailing. The learning curve is somewhat steep. Any thoughts on leaving the ballast out, besides the obvious effect on trim?
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Old 04-03-2023, 10:16 AM   #35
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A lighter boat may have better fuel economy, but having the propeller higher in the water may mitigate that some. A heavier boat may be more stable in a seaway. Weights all the way forward or aft will increase pitching, but may slow it down a little.


Bottom line -- I'd check the waterline with all tanks full and empty and if you're OK with it in both conditions, leave the sandbags out. If you decide to put them back, dry the sand thoroughly and put them in heavy plastic, so they don't absorb moisture. If yours is an early 1973 -- wood -- I would be reluctant to have even plastic wrapped sandbags against the hull -- both because it will trap moisture and because any weight on the inside of the hull has a small tendency to loosen the fastenings.


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Old 04-03-2023, 10:22 AM   #36
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Thanks for that. The sand bags were in tough shape. I was thinking that if it turned out I'd be better of with the ballast that I'd use concrete. Good tip about checking the water line loaded and unloaded. The boat is glass, and a lot of it. First year they used fiberglass. Thanks again.
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Old 04-03-2023, 10:50 AM   #37
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Greetings,
Mr. r. As Mr. C suggested, check where she sits with fuel tanks empty/full. Then act accordingly. It may be that IF you have to add ballast you might purchase some heavy plastic bins and fill with ??? to achieve your desired ride. The fill chosen would determine amount (sand/lead shot/iron bars???). One problem I can foresee is how would you hold said bins in place? Glue them to the hull? Install cross bracing?

One advantage, IMO opinion, of using bins is you can add or subtract fill to optimum amount.


Our 46' Cheoy Lee had 8000lbs of ballast (I read that figure somewhere) most being far aft but some just aft of midships on the star'bd side. Iron or steel ingots that must have weighed 100+ pounds apiece. Well contained within a pocket in the laz'.
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Old 04-03-2023, 01:28 PM   #38
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Thanks for the ideas. I plan to see what happens with no ballast, then add and test those results. There are 2 pockets between hull & stringers at the transom where the bags were. I will put concrete there as needed.
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Old 04-03-2023, 02:15 PM   #39
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Willards were ballasted with concrete and scrap steel pieces as aggregate. The risk in getting it wet is if the steel rusts, it will expand and disintegrate the concrete.

Willards carried a lot of ballast - almost 25% of their design displacement. I believe the steel/concrete mix is significantly heavier than plain concrete. If you need to re-ballast, you'll want to find some lead as concrete may not do the trick.

I recently added a bow thruster and removed ballast in forward keel. I removed 800 kgs of concrete/steel and replaced with 650 kgs lead. It was amazing how much weight she could take. I'll still need some trim ballast once half-load fuel and water with stores.

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Old 04-03-2023, 02:24 PM   #40
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In a previous boat I added about 600 pounds of lead ballast trying to bring the stern down so things would drain properly. I bought 60 pound or so ingots. Then laid them in the stern and glassed over them for 2 reasons, one to secure them and two to contain any lead that might flake off. Worked very well. Lead is so much denser than concrete it will take up less space but it will be more expensive than concrete.
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