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yabasayo

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  1. Save yourself a lot of potential issues and cost and walk away. Also overplating side plates raises the centre of gravity of the boat and reduces stability. You will be able to find a boat in better condition.
  2. Either slag inclusion in poor quality steel plate (very common) or SRBs, or both. Sulphate reducing bacteria occurs in low oxygen stagnant environments, and produces hydrogen sulphide which attacks iron and steel. Slag inclusion can lead to the formation of small galvanic cells due to the proximity of different materials in the steel. These in turn can give rise to galvanic corrosion and pitting. Galvanic corrosion can also be cause by faulty electrical equipment on the boat. On the other hand it could just be a poorly painted area which has rusted a bit more than the surrounding material.
  3. As a retired naval architect and marine engineer I'll give it one last try. In this case, the mass moment of inertia (which I presume is what you are now talking about) is a resistance of the boat to radial acceleration. In other words it is a component of the speed at which the boat rolls and recovers, but not the extent to which it rolls, for given force at a given vertical distance from the axis of rotation. This is complicated by the fact that a certain amount of water also moves with the boat effectively adding to the mass. The amount a boat heels when loaded to one side or other of the centre of buoyancy, effectively the boat's centre line, depends totally on the Righting Moment. End of conversation.
  4. Quoting basic applied mechanics is not dimensional analysis. Can you explain how your incomplete statement proves anything. You apparently do not understand that in the case under discussion, mass refers to the centre of mass of the whole boat and whatever it contains. To make it simple, if you have a 10 metre pole with a 1 kg weight at each end, the centre of mass is half way along the pole ie 5 m from each end. If your pole is 20m long with a weight a 1kg weight each end, the centre of mass is still half way along the pole. So if the equal weights at each end of the imaginary pole represent the ballast, you can see that both weights combined can be said to act through a point half way along the pole. (if you can't accept that then I give up) The boat rotates around the centre of buoyancy (which itself moves as the boat lists). Length here is the horizontal distance between the combined centre of mass and the centre of bouyancy.
  5. The only way to "make it slower to tilt" is to increase the Righting Moment.
  6. Your response does indeed make me think of a dumbell What you call the 'moment of inertia' is for a floating vessel, the Righting Moment, and is expressed in tonne metres. So to claim that "it wouldn't affect the righting moment, but would make it less tender" is a contradiction and an impossibility. 'Tenderness' is the manifestation of the Righting Moment and nothing else.
  7. Sorry old chap but there is some unnecessary confusion here. Given that everything else is constant (fixed), Inertia is directly proportional to mass (of the whole displacement, not just the ballast) Therefore, yes, by adding ballast you are increasing the inertia slightly. However, as discussed earlier, the whole mass can be considered to act through a single point. So moving the ballast around while maintaining zero list and the required trim, ie moving it symmetrically around the current centre of gravity, alters nothing.
  8. I believe it makes no difference. The hull shape is obviously fixed so all you can do with ballast is alter the centre of mass of the boat ie given that you don't want any angle of heel you can only move the centre of mass vertically. The centre of mass is a combination of the the weight of the structure and everything in it, plus the ballast you are adding and acts through a single point. If for example you add 1 kg of ballast at an equal distance from the centreline on each opposite side of the boat, the centre of mass of the combined 2 kg is on the centreline of the boat.
  9. I personally wouldn't consider paying them anything until the boat is complete and ready for delivery. If theirs is a viable business they should be able to borrow the money from their own bank.
  10. Not an exact science. Erosion rate of the anode is not linear and depends on its surface area and condition. The anode would be far less effective when it reaches year 10 of your example than it was when new. For those reasons anodes should be replaced when they have lost around 60% of their mass.
  11. Fill the tank to the brim (up the breather) before welding. Have a foam extinguisher handy just in case you penetrate the tank whilst welding. Never weld on a empty tank.
  12. Sounds like you're nearly there. I'm surprised you can get 2.48kw from solar panels though. You must have something like 20m2 of panels. Presumably you've cut your prop down on a lathe ? If so you must have some pretty horrible blade profiles. Once settled on an optimum size you should get an increase in performance by buying a new prop.
  13. Shot blast, hot zinc spray then epoxy - then forget for 10 years or more.
  14. This makes sense to me. I have drilled quite a few holes in my boat (not the baseplate I must add ) and over my life time have drilled a lot of holes in steel and have often felt I go through hard, soft and crunchy bits. Only last week I was drilling some holes in the boat and after a couple of easy ones the drill bit suddenly jumped and snapped, and I know it was a really good bit because I got a whole packet of them for £3 at Screwfix. ................Dave Both above correct in my view. That's why you should have a certificate of origin and quality for steel supplied for a new boat build. See thread on Steel quality and origin in build blog.
  15. Guess what - you have reduced the prop area by about 30% and the rpm has increased by about 30% ie from 900 to 1200 rpm. I think you said the motor should run at 1650 rpm. On that basis you need to reduce the prop area by about another 25% or down to about 14 inches diameter to get your desired full load rpm. As I pointed to in post #41, your prop was overloading your motor by about 100%. Reducing the prop area by a total of 50% or so fixes that.
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