hypothetical question, how much weight could my boat safely hold?

[Chinook92]

hypothetical question with no serious intent beyond general musing


i have a catalina 27, basic run of the mill boat

how much weight could that boat hold before its unsafe?

if i fiberglassed up the cockpit locker and made it water tight and insulated it would the boat still be stable if i filled it with say, ice? for an extended fishing trip? if i glassed up the quarter berth and made the two lockers identical, could the boat safely haul that much? boat is going to have a 20 horsepower Yanmar Diesel, and chances are after a few days that ice is going to turn to water and get pumped over the side, so its a depreciating factor, longer time goes on, the less weight there will be, as ice weighs more than fish per volume anyhow

thinking my c27 might make an economical little utility knock-around boat, maybe something that can squeak by off shore for a few days when the tuna get near, run out, fish, drift at night, fish again, and head home when the weathers nice, the fuel bill would certainly be appreciated

[psk125]

Weight is important, but is not the only factor in safety. If you figure that the boat is designed to have berths for five, and the Coast Guard figures an average person weighs 185 pounds, that gives you 925 pounds. Don't forget that includes the weight of you, the skipper, and any crew. Where the weight goes is important as well. Too far forward and it's called submarining when the bow doesn't rise up over the next wave...or any after that. Too far aft and the stern gets buried in a welter of foam that sweeps forward and smashes in the companionway hatch, with the same result as too much weight forward. Are the bulkheads and cockpit structures strong enough the bear the weight being considered, or will they need reinforcing? Will the weight make the boat top-heavy? Ask the Swedes about the Vasa. It might be worth experimenting with smaller amounts of ice and shorter trips in good weather to see how the boat handles and what works.

[Don C L]

Hmm, ok I'll muse along...My friends have a one right next to me. The Cat 27 is not a hull designed or intended to take a whole lot more weight. But that said, you could add a lot and it will still float fine, they have a good deal of hull volume aft, but may not be as stable, as you allude. The cockpit can hold 6 people or more, but it wasn't really intended to sail that way, (but people do it all the time.) 6 people could be 1200 lbs of so. depending on your friends. First you are adding a lot of weight to the stern, and if I understand correctly, a good portion of that will be above the waterline. In addition as ice melts and becomes water it will become a free surface, ballast that is free to move, which does the stability of a boat no good at all. So, don't let water slosh around in there. So I'd have to see the boat but if the weight is raising the center of gravity then it is working against the righting force of the keel. Also, with the weight aft it also aggravates instability. The more the weight moves fore or aft, the more easily the boat will roll because less of the stability the hull affords is at play, if that makes sense. So I have not answered your question, but I imagine, as long as you don't take any friends, you could put 1200 lbs or so back there and be ok. But how big are the tuna you are going to put in there?
Oh and then there is the issue of the exhaust being underwater.

[Tetepare]

The bow is effectively sealed. I’d pack all the ice and tuna in the bow, and motor backwards.

[Adelie]

I would guess you would be OK with 2500lb added: crew, provisions, cargo, weight of modifications.

A large cargo weight such as you indicate should be added near the longitudinal center or the boat, ie the main cabin. Adding 1,000lb near the bow or stern will create significant problems with trim and stability without even getting into issues of hobby horsing.