Alberg 30 complete gut and restoration! Question of balancing the boat weight wise

Discussion in 'Sailboats' started by wesley Sherman, Dec 8, 2020.

  1. wesley Sherman
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    wesley Sherman Junior Member

    I have Installed 6 bulkheads and a chain locker. Going forward how does one determine how to balance out the boat.

    I am searching for information about where my boat's sail center of effort would be. Is there any correlation of the center of effort for the sail and balancing the boat? Or does one balance weight by just the boat length or apparent cent of the boat.

    As I go forward building and installing things like engine, fuel tank, water tanks how does one make sure not to overbalance the boat forward or aft? Also things like the anchor chains, windlass and more. The last thing I want is to not get it right and squat in the water with my freeboard and or too high freeboard

    I currently have estimated the remaining woodwork forward of the main bulkheads and the weight of the woodwork behind the main bulkheads.. Pretty much of everything but now how to place balance out of the water.

    I know this is probably common knowledge but to me it new. I have weight all teak all fiberglass and keep a log of approx oz's of resin as I layout.

    I should add I do realize I will balance the boat to some degree after it floats with gear and equipment..

    Thank for your help

    I have made sure that the bulkheads have the same amount of wood weight on either side of the hull.

    I am probably overthinking.
     
    Last edited: Dec 8, 2020
  2. bajansailor
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    bajansailor Marine Surveyor

    I think that you are probably overthinking it all a bit Wesley - but that is much better than underthinking it!

    Re the boat's sail centre of effort - on the sail plan shown here - https://sailboatdata.com/sailboat/alberg-30
    It mentions the centre of area for the combined jib and mainsail (410 sq ft) just aft of the mast.
    This appears to have a 'lead' over the centre of area of the side profile of the keel - which is good, you want to have that.
    What complicates things a bit is that the hydrodynamic centre of lateral resistance (CLR) of the hull below the waterline is not in a fixed position - it tends to wander about as the boat heels.

    Re all the extra weight that you are adding, do you have a rough idea as to how much your gutted hull weighed before you started adding new bulkheads etc?
    If you start with the gutted hull, and have a rough idea of the weight of it, and where the centre of gravity will be, then you can take moments about a suitable datum point for each extra item that you add.
    This datum could typically be the transom, or perhaps the aft end of the waterline.
    The moment is the weight of an item, multiplied by the lever which will be the distance of the centre of gravity of the item from your datum point.

    So we will end up with an equation something like this :

    Final displacement x lever arm = (hull shell weight x lever arm) + (W1 x d1) + (W2 x d2) etc

    Where the W's are weights of the individual items that you have added, and the d's are the levers (the distances from the datum point).

    The final displacement will be the sum total of the hull shell weight and all the additional weights added.

    Hence the only unknown is the lever arm for the final displacement, which can be calculated from the equation.

    If this is pretty close to the distance of the estimated centre of buoyancy of the hull from the datum, then she will float fairly level.

    And if the sum total of all your weights adds up to approx 9,000 lbs (the design displacement, according to Sailboat Data), then you will be floating approximately on the design waterline.

    Be aware that if you use the aft end of the LWL as your datum, and you add a weight in the Lazarette locker (which is aft of the datum), then the lever will be negative rather than positive, as it will be acting the other way.
     
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  3. fallguy
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    fallguy Senior Member

    I read somewhere that dynamic loads need to be closer to center.

    And I don't think you are overthinking.

    In some boats, each weight is calculated in a lever moment spreadsheet.

    For example, if you place a water tank all the way to the front of the bow; that lever is about 14 feet times the mass of the tank. Then an offsetting weight(s) would be needed on the other side.

    The reason the dynamic weights are centered is so their change has less change on those moments.

    others here are far better versed than me on the subject, but I think you are on a good path paying close attention
     
  4. wesley Sherman
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    wesley Sherman Junior Member

    Exactly what the boat weighs has to be a close assumption. When the boat was brought home we stopped and had the boat and trailer weighed at a scale at the local recycling depot where A friend works. The trailer was weighed after and we came up with 8643lbs That was with the motor and fuel was in the tank and the mast was tied to the deck. I don't know what the hull weighed after stripping bare. But I do know that so far I have installed the 6 bulkheads, Vlocker bulkhead pulse various other pieces of marine wood. We have a total weight of 146.77 lbs. 3 gallons of Resin and hardener at a weight of 11.23lbs for 33.69lbs. Fiberglass 1708 at 15.62lbs. Fiberglass 17oz at 6.68lbs. Mast step beam at 56.25lbs.

    So at the moment, I have an addition of 259.01 lbs into the hull. I estimate the rest of the interior work to be about 2.2 x more than I've done so far for a total of approx 600lbs total.

    The boat was empty when we weighed it other than the cooktop weighed nothing so I would guess the boat at 8643 - Engine and transmission 335.25 - aluminum tank at 138.54lbs (tank and fuel) - estimated interior woodwork of -600lbs. Then there was the head and plumbing at 88lbs. The icebox was 32lbs, We weighed all the rope and sails that were on the boat that came up to 98lbs of rope and 168lbs of sails, sadly unusable. 246lbs of trash ie. cushions and clothes extra gear etc...

    So we come up with a total of 6938 approx of the bare hull.

    Why did I do all this because I wanted to know how much weight was in the boat to try and make sure port and starboard were approximately balanced when putting it back together. I was more concerned about the balancing of the freeboard that I didn't want to squat more than Alberg squats already. Again I have to say I am often way overboard in overthinking. I was trying to make sure I didn't miss anything that would bite my *** later. To much data is better than no data right?

    So since most of my planned changes other than the engine and tank, more of the weight of the changes I am making more weight will be amassed right behind the bulkhead in the cabin, ie galley cold box refer counter etc. I guess this is a better thing centering more weight in the center of the hull?

    Banjan are you saying that I should find the balance spot of the hull (where the weight of the boat is the balance fore and aft equally?) This we can do easily if this is what you mean in order to find the datum point? This point is used to help calculate the balance overall?

    You mentioned something Banjan and fallguy that has been on my mind. For example, if the center of the boat weight-wise is found, And the engine is 335lbs and 6' from the center of the boat or Balance point fore and aft, do I then need to think about the counterbalance weight 6' forward. I mean not to be exact and perfect but generally close to a balance from this balance point location. Kinda like a playground see saw general balance equal distance from the center.

    Thank you all for your input and help. This is a first-time project of this magnitude and I don't want to miss something simple and catch it too late
     
  5. fallguy
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    fallguy Senior Member

    All the weights and dimensions go into a spreadsheet as lever moments.

    So, for example, water tank full centered at 2' forward and mass 170 pounds is a moment of 340 forward.

    Fuel tank 3' aft of center and weighs 100 pounds. Then you know that moment is 300 the other way. And you have a net of a 40 pound moment aft.

    And you have a bow anchor on a pulpit with a 25 pound anchor and roller and it is 16 feet forward of the center. Thus a 400 ftlb moment offsetting the 40 aft for a net of 360 forward.

    Etc.

    I am a novice builder, but this is the approach I use.

    When you get to the finish line; it is always nice to have a few movables for fine tuning in real life. I also find my boat gains weight annually and try to do an annual weight reduction of unneeded xtras. Like that extra roll of duct tape you bought when you couldn't find the other one.
     
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  6. wesley Sherman
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    wesley Sherman Junior Member

    This is great fallguy! Just what I needed... Helps me figure out a lot of stuff. I have to find a way to figure out the weight of my mast however, according to Rig Rite mast section cross-section info.. my mast should only weigh 3.44 lbs per foot x35' = 120 ish lbs and this is in fact not possible. As myself and two of my friends toted this thing over a hundred feet to my container and we bitched about the weight. So need to figure out how to weigh this thing.

    Thank you again everyone for the great info.
     
  7. fallguy
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    fallguy Senior Member

    what mast?
     
  8. wesley Sherman
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    wesley Sherman Junior Member

    The mast that goes on my boat
     
  9. fallguy
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    fallguy Senior Member

    What specific mast Wesley?

    Rig rite carries sparcraft masts among others. The datasheets are easy to find.
     
  10. tlouth7
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    tlouth7 Senior Member

    Can you get the boat in the water? If so you could load her up with weights, plus a couple of bodies in the cockpit, to bring her to her lines. Measure where the weights have to sit for-and-aft to achieve this, then make sure all the things you add have a centre of mass in the same position (roughly). If you know that the design tends to squat then you could bias things forward a little.

    Otherwise is there anything that you could adjust after the fact? For example if the water tanks go under the saloon bunks then you could play around with those once you have her sailing. Equally you could choose the battery location based on initial results.
     
  11. wesley Sherman
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    wesley Sherman Junior Member

    Main sail Mast.

    No "tlouth" boat won't float till I am done. But yes Somethings can wait to be placed to some degree. I realize I cant estimate everything and its position but as FallGuy explained about calculating weight placement in a previous post.
    All this new information has brought me to another question. Being that the Alberg length of the actual water line is I think 26.6' I am thinking that maybe when calculating weight placement should be mostly within the waterline area of the boat. Is the center of mass basically in this area? Maybe most of the heavyweight placement should be within and balanced in this area that is actually in the water? Make any sense? The center of this WL area is where the bulk of weight should be centered then moved outward? From the actual drawings of the boat, the center of the waterline area is just slightly forward of the center of the cabin.
    Being that the chain locker and the aft well locker would and could be used to balance out any of the remaining balancing issues? As "tlouth" suggested I could then adjust the placement of items ie moving fore or aft the fuel tanks that would be in the port and starboard cockpit lockers.
    I appreciate all the info and help everyone has given, helps to sort out things that don't come easy or from experience.
     
  12. fallguy
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    fallguy Senior Member

    I believe you are asking about the vertical aspect of the weights.

    I think the general wish is for the weights to be lower.

    Weights up higher contribute to stability concerns. There are different types of stability.

    Weights on the ends contribute to pitching moments.

    Weights on the outside edges contribute to decreased roll if by waterline. But I don't know how well

    I don't profess any expertise on these.

    Hopefully another poster will coin in after my half assed answer.
     
  13. bajansailor
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    bajansailor Marine Surveyor

    It is good to try to keep heavy weights out of the ends wherever possible, and as low down as possible.
    You are not going to make her 'too stiff', no matter how hard you try.

    Instead of stowing your chain cable right up forward in the chain locker, you could have a hawse pipe just forward of the cabin, coming down to that stowage locker between the forward berths (as shown in the GA drawing on the Sailboat Data page). How much chain do you intend to carry?

    I wouldn't worry too much if the boat ends up trimming down slightly by the stern when you launch her - she will do this anyway with the weight of you (and any crew members) in the cockpit. And a bit of stern trim is a benefit re directional stability (so long as it is not excessive).
     
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  14. tlouth7
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    tlouth7 Senior Member

    If you can't get the boat in the water, and you don't know the fore-and-aft distribution of the weight that you pulled out then it is going to be hard to get the trim spot on. It is not enough to put the centre of mass of the stuff you are adding at the centre of the waterplane; what if the empty hull + spars have their weight biased forward? You would need to correct by biasing the added weight aft.

    The safest thing is to build the new interior to match the original as much as possible. Especially with regard to engine, tank and battery locations. Most of the joinery is likely to be close to the centre so exact design of this will have minimal effect. If you want one element to deviate from the original layout (e.g. engine further forwards) then pair this with a corresponding movement of something else (e.g. move the batteries aft). You can balance this effect without needing to know the overall mass distribution.

    If you can make the new interior lighter than the original and then bring the boat down to her lines with ballast in the bilges then that gives you lots of freedom to adjust trim, with the bonus that you will be moving the overall CoG downwards which is always a good thing.
     

  15. wesley Sherman
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    wesley Sherman Junior Member

    The engine will be in the same location, Fuel tank will be now two tanks on either side of the cockpit with baffles and a connected line to equal out the fuel level. The galley will be moved forward to the cabin bulkhead, Starboard side, Portside will be the icebox and cabinets. Either side of the companionway will be the port and starboard settees. The anchor rode will not reside in the forward chain locker but just in an accessible locker just over and forward of the keel. We built one of these on a friend h30 with a couple of keel rollers where it comes out of the channel to be pulled up by the winch. Worked out very well, he has been extremely happy with it. There is a good amount of chain fall for it to work well. There is an access panel at the lower end where you can open it and pull the chain fully down the channel it runs through when getting underway.

    I have a fairly new 5/16 ht anchor chain 240' about 250lbs I think, this is why I need it to chain fall further into the boat closer to the waterline. With all the information I have received I think I will be ok with the plan I have in place. There will be a few things I will not place until I get her floated as has been suggested.

    I am now curious from what fallguy said "Weights on the outside edges contribute to decreased roll if by waterline" Is this a good thing or a bad thing. Theoretically, if I had an 8" diameter tube 8' long Filled with say fuel or water. This placed either side of the center of the boat at the waterline. What effects would this have on the boat at sail? Each weighing 70lbs. What about higher than waterline? another 12" higher? ( Tank would be baffled.)
     
    Last edited: Dec 11, 2020
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