Adding keel weight to small houseboat

[fallguy]

Could also add bilge keels…not sure about the design, but probably something above the planing area of the hull that when the hull sinks or ballast is added also dampens roll.

 

[silentneko]

Usually, mass is added to the outside edges to dampen roll, from my limited understanding.

The location you chose would not be ideal.

I believe two saddle tanks on the outside edges that can be emptied would be better.

A keel is offset by a mast to dampen the roll. If you don’t have a mast, a keel mass increases the roll, from my understanding. I believe it becomes a pendulum with no counteracting mass. This is experienced in real life by dismasted vessels or vessels traveling to get their masts added.

So, the better plan is to use ballast tanks, I believe on the sides. When underway, or say in bad weather; you drain them, and you flood them for overnight to dampen under typical chop. Probably something like 20 gallons a side or maybe only 10-15.

Hopefully, someone credentialed will reply. I think if you post the immersion rating of the hull, it would make people more comfortable. Noone wants to help you sink, eh?

Now, I suppose you may argue the hardtop is like a mast, but it isn’t. The mass is too spread out.

You can test the theory I’ve offered easily.

Take the boat to a dock and put 4 sand tubes in the middle of the boat, say 200 pounds. Push the side of the boat down a given amount and release it and count how many times the boat rocks before practical rest. Then take the tubes and put 100 pounds on each outside edge and repeat the test. Pretty sure the outside edge will be less time/less cycles to get to rest.

Sorry, I got tied up with some things and didn't get a chance to do some figuring since most of my notes are across town in the warehouse. There isn't a whole lot of info on this hull as it was only made for a short period. From what I can tell looking at some old photos and the few manufaturer pictures I could find the designed draft was between 7 to 9 inches depending on load and balancing. This was with the hull weight at 975lbs. Rough calcs put the displacement at 7" around 2400lbs conservatively with a PPI of 350lbs+/-.

I think your note about weight central vs saddled is interesting and not something I've really considered. I can't test the theory with the hull as it's on supports, and won't be moved until the floor is foamed in and secured. Ballast tanks are not an option on a hull this small with limited room, and would add more complication then I'm willing to get into. I've got some inquires out to a few guys who have done terminal trawler conversions and I'll let you know if they respond with anything decent. Either way I need to decide soon as the foam has arrived.

 

[silentneko]

My thoughts, having considered C.G. impacts on my current project. . . .

Make the camper piece as light as possible

Design the boat furnishing and components so that as much weight is as low as possible

Consider water ballast, if needed.

Being wider (beam) will allow you to be taller (camper)

Everything will be built very lightly. I'm struggling mentally with that since I like to over build, lol. The base hull when done will be much lighter then originally built. They used DF 3/4" for the stringers, transom and deck, and the console was reduculously heavy. Once stripped the actual thin fiberglass shell weighed very little. That is part of the reason why I am considering adding weight back.

 

[silentneko]

Could also add bilge keels…not sure about the design, but probably something above the planing area of the hull that when the hull sinks or ballast is added also dampens roll.

No planing. I'm planning on a smaller outboard and displacement speeds of around 6.5mph. Bilge keels are possible and wouldn't to hard.

 

[fallguy]

Everything will be built very lightly. I'm struggling mentally with that since I like to over build, lol. The base hull when done will be much lighter then originally built. They used DF 3/4" for the stringers, transom and deck, and the console was reduculously heavy. Once stripped the actual thin fiberglass shell weighed very little. That is part of the reason why I am considering adding weight back.

What did you ‘strip’ out? A thin glass hull may have needed support.

You should trust me on not adding keel weights; it is the wrong way to go. A trawler is built with a deeper vee, in general, and ballast is sometimes added to get to dwl. Your hull shape will not benefit from central weights along the keel. Whoever told you this is broad brushing the concept across all hulls.

 

[silentneko]

What did you ‘strip’ out? A thin glass hull may have needed support.

You should trust me on not adding keel weights; it is the wrong way to go. A trawler is built with a deeper vee, in general, and ballast is sometimes added to get to dwl. Your hull shape will not benefit from central weights along the keel. Whoever told you this is broad brushing the concept across all hulls.

It is a very thin glass hull. I bought it because for it's size I thought it would be a decently beefy hull given the weight. All the info I could find on them and the similar kenners were that they were tanks. Come to find out differently. The hull had a good twist in it too. After I replaced the transom, the floors and stringers were removed. I built a support structure under the hull to support and level it while I rebuild. The foam and floors are the last part of that step. I feel the foam is definitely needed to support the hull, like a Whaler.

I don't disagree with your assessment, I just didn't really consider it. In my world, planing power boats, it's all about reducing weight, never adding it, for shallow draft. I think I'll skip the weight all together.