It can vary a lot but very few powerboats (almost none) have a VCG below waterline. In smaller (< 60') ballasted full displacement boats that are not steel or 2+ stories high, VCG will be 1-2' above waterline. In un-ballasted semi displacement boats VCG might be 3-4' above waterline. Fiberglass boats will generally have a lower VCG, steel or aluminum (if the deck and house are metal) will be higher.
This is great information thank you, and exactly why I was thinking an expert should have some input here. The point still remains the same. Even if the CG is too high, and the boat is stable at rest in calm waters unloaded, that can change very quickly in poor sea conditions and variable loads. I know this is true of any vessel engineered or back yard mechanic built. Rolling over is only a worst case scenario. Trim is important. Most of us take trim for granted, because our factory build vessel was engineered, and test for trim.
None of this takes anything away from Mat, or the amazing amount of great work he has accomplished. This is merely friendly suggestion from a fellow boat builder that has had his issues over the years. Any boat no mater who build it should have critical evaluation of its trim and stability when any significant amount of change had been made.
True story.. from a fisherman..lol
I was on a fishing trip this last year with one of my customers. We added a 60 gall live bait tank and a 32 cubic foot fish box to a 1972 Uniflite Salty Dog. The owner had me go out with him for tuna with a few of his buddy's.
At the dock this boat is a rock. What I did not know is that 7 more guys all weighting in at of 250 pounds were showing up with all their gear. I was nervous, and I had a discussion about weight with the boat owner, but the owner assured my that this boat was fine with lots of weight..... We headed out 70 plus miles off shore. The weather was good 5 foot seas on 13 second interval. We found the tuna... That was all fine and great until all 7 big guys wanted to have a look at that fist fish. We rolled sharply to the port. The self bailing scuppers on the port side buried under the water, and we were now taking on several hundred gallons a minute of blue water. The force of the on the swim step ripped the swim step off the boat. Everyone got back to stable positions on deck. Orders were given that no more than 2 crew could be on the rail at any give time. We finished the trip with 28 tuna, and a dry boat.
See the addition of the live well added 500 ponds to the boat at the after most part of the deck well above the CG (this is very live weight!). The Fish box below deck (at CG) added another 800 pounds (again live weight, and before any tuna) to the boat. The owner was used to having 2500 pounds of fisherman, and 500 pounds of gear on board, but did not calculate in the additional 1300 pounds of water, ice and equipment. Cool heads kept us from sinking that day, but had the seas been bad...(50 degree waters)... we all might have died!!!!! The Salty Dog is a great boat, and capable of caring large loads no problem. I think the crew limit for that boat is now capped at 6! Scupper flappers were added. We doubled the bilge pump capacity, now they manage the live tank levels per sea conditions. He loves the mods we did to the boat, but was not fully prepared for how they wound change they way he uses his boat.
Just about the time you think you have the upper hand on boating it will bite you in the butt!
