Viking Norsafe 90 people Lifeboat Mods

Discussion in 'Boat Design' started by Emic, Jun 22, 2022.

  1. Emic
    Joined: Jun 2022
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    Location: Malaysia

    Emic Junior Member

    Dear All
    I am thinking of purchasing a Lifeboat and modify it as per drawings. Its a project and could be fun.
    IMG-20220622-WA0010.jpg
    I would want to modify as per the drawing below
    IMG-20220531-WA0029.jpg
    As it has a total weight of about 5000kg and it needs to carry 90 people at 82.5kg per person it will be a bit of a cork in choppy waters. Extra tankage will be added...approximately 800+ lt of diesel and 500 lt of water. An internal fit out etc...however i would like to add a keel. I am thinking of layers of 3" galvanized iron bars bolted to the main keel and to each others and encapsulated in GRP.
    Screenshot_20220622-212138_Acrobat for Samsung.jpg
    Roughly as per the red keel on the drawing above.
    The boat already has a positive stability up to 180 degrees and i am actually thinking at ways to make it less bouncy/corky in bigger seas. What do you guys think would be a proper keel design / weight to achieve a smoother ride? All comments and suggestions are more then welcome. Am i being silly with this project? A friend tells me i should never modify a hull as they are designed for a purpose and by doing so i will just waste money and ruin a boat...therefore i ask you :)
    Thank you
    IMG-20220523-WA0023.jpg
     

    Attached Files:

  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum Emic.

    Have you seen this long thread on the Forum about enclosed lifeboats?
    What could be done with an enclosed lifeboat? https://www.boatdesign.net/threads/what-could-be-done-with-an-enclosed-lifeboat.63238/

    Stodig is mentioned in this thread - here is her website :
    Stødig https://arctic-lifeboat.com/

    Her re-fit was carried out by two architects who have done an excellent job.
    They do not appear to have put a keel on Stodig, and they have travelled impressive distances with her.

    Re how your boat already has positive stability to 180 degrees, if you add a heavy keel then that will just make her even more stable, and even more 'jerky', with a quicker roll period. Rather than adding weight in a keel, it might be better to add tankage and outfit weight in the hull, so that the overall centre of gravity is raised a bit, which will improve the motion and increase the roll period.
    You basically have about 7 tonnes to play with, re the 90 pax at 82 kg each, so you can use this as a basis to design your accommodation layout and tank capacities. But be careful, as weights can easily add up very quickly.
     
    Last edited: Jun 22, 2022
  3. Emic
    Joined: Jun 2022
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    Emic Junior Member

    Hi bajansailor....thanks for your quick reply...
    Yes i had a look at Stodig...hence the idea when i bumped into the lifeboat for sale here in South east Asia. Watching Stodig videos they were doing a crossing and the boat was kinda bouncy...footage was very brief :) and there is very little available on google on sailing around on Lifeboats. I get your point in your advise to start off with a well planned tankage and added weight down the bilge. what would you consider the hull design to be... displacement hull? Flat bottomish kind of ??? lol. If i understand u correctly an additional external keel will increase the side to side motion in case of side waves by righting the boat up too fast...am i correct? Any other ways of achieving a smooth ride in typical 1 mt waves calmish sea conditions? Would adding bladder water tanks at midship inside the side benches ( currently filled with foam ) help or make it worse? thanks
    aa.jpg
     
    Last edited: Jun 22, 2022
  4. bajansailor
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    bajansailor Marine Surveyor

    Yes, the hull form is definitely a very full displacement type .
    If you add an external ballast keel you might make her 'too stable' where she has a very quick (and possibly uncomfortable) roll motion.
    Whereas a slower roll motion will generally be more comfortable, all else being equal.

    I think that any displacement hull form of this size will be experiencing noticeable motion in 1 metre waves - how 'smooth' is smooth?
    She has quite a bluff bow, so in head seas she is not going to 'cut through' waves too easily.
    And with the seas on the beam she will probably roll a bit, like pretty much any other displacement boat - you just want to then find the most comfortable roll period.

    Re adding bladder water tanks under the benches, bear in mind that the centre of gravity of the 7 tonnes of passengers might be about 1' (or thereabouts) above the benches (when everybody is sitting down) - and this is the weight that you really need to compensate for, not only with water, fuel, equipment and stores, but also the weight of all the outfit (like furniture, bunks, galley etc).
     
  5. Emic
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    Emic Junior Member

    Thank you sir :) hopefully it wont turn into a throw up box.....as they come with plenty of sea sick meds ;)
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I only have a minute or two.

    Moving some of the tankage to the sides near the waterline may dampen the roll. But this is really not my specialty. Also, rather than the deep keel, bilge keels may be more bang for the buck, but also not expert enough to advise beyond mentioning as a possible.

    These boats have been redone; sometimes, Not so well. I don't understand your cross section well.

    They are so big, a considerable aft cockpit/outdoor area seems sensible to me. And if you plan to go above, then the round top is dangerous.
     
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  7. Emic
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    Emic Junior Member

    Hi FallGuy... I am planning to lower the round upper deck by as much as comfy headroom will allow so probably a foot foot n a half. That will create a nice flat deck on top. Even lower level at the front to create an additional flat deck for a couple of mattresses and an anchor locker/windlass spot. That will be above a forward open cabin/bed. Thanks for your reply !
     
  8. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Changing the superstructure shape may ruin the vessel's self-righting ability, unless you compensate for the removed volume somehow. As for the supposed quick roll: first you are referring to subjective observations without numbers backing. There should be test figures available for roll and pitch periods; with these at hand we can discuss "good and bad". Second: 1m waves were never a concern for the (relative) comfort in these boats, but rather the movements in really rough stuff.

    That means that the boat should not have too long a roll period making it roll in resonance with the big waves encountered, because that would risk repeated rollovers, and that is uncomfortable, believe me! Now if you move some weight up along the sides, you will be able to reduce the roll frequency slightly, without disturbing the center of mass to much, as noticed by bajansailor. His comments on the keel are wise as well; you don't want to increase stiffness, a keel is only needed as a lateral plane for sailing. However, you might consider bilge keels for their ability to dampen rolling motions.

    Edit: Btw, the hulls in the photo's are not the same hull shape as your sketches, beware!!
     
    Last edited: Jun 23, 2022
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  9. fallguy
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    fallguy Senior Member

    The round top is dangerous to walk on! Not for the r.m.!
     
  10. baeckmo
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    baeckmo Hydrodynamics

    ....meaning what?
    The rounded top structure is there to make absolute certain that the hull will NOT be stable upside-down. If you want a promenade trail on top, there are other solutions.
     
  11. fallguy
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    fallguy Senior Member

    I said earlier the top was unsafe, but not in regards to righting. It was not designed for walking..
     

  12. Emic
    Joined: Jun 2022
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    Emic Junior Member

    Thank you for your observation and especially the above. I have not yet inspected the vessel but is being sold as a meggie 10.7 from Viking Norsafe...hence i was able to pull these drawings from their website. I will keep an eye out at inspection time, would be an absolute bummer if its not.
    My apologies as i will not be able to provide specific numbers for roll n pitch as I m not that advanced in my knowledge of boating. The fact that cutting down the round top deck to make it a flat deck will impair the boat ability to self right itself is an eye opener and thank you for that. Maybe a foam filled tank shaped structure on one side of the rear canopy could aid to tilt it enough to commence the self righting?? aaa.png
    Dear Fallguy... i want to chop off the rounded top and by doing so make it flat...I intend to leave about 6'+ of headroom inside the boat, all subject to measurements and inspection but it will not be a round top, that would be asking for trouble. may even give it a good go with anti skid paint just to make sure.
    BB.png BBB.png
     
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