Latest News: Forums Technical Matt or Shiny?

  • This topic is empty.
Viewing 9 posts - 1 through 9 (of 9 total)
  • AUTHOR
    POSTS
  • #4024
    admin
    Member

    Is it me or has this Forum gone very quiet of late?

    After a forced break while I explored the pleasures of Swine Flu, finally got back to painting Kes, my MkII GRP boat (4137)

    I had already laid one coat of finish over an epoxy primer and two coats of undercoat. Rubbing down was tedious and rather disappointing as the boat went back to looking rather shabby, but today I have brought back the colour and shine (see pics).

    Which made me start to wonder…

    I have heard that a slightly matt finish is better below the water-line, something to do with micro-turbulence making the hull more slippery as the surface layer of water cannot stick to the surface of the hull.

    Any fluid dynamicists out there?

    #8687
    Anonymous
    Inactive

    Hi Mike.
    I’d also noticed it’s been pretty quiet. I was going to do the mucky bottom cruise on the Humber, Without warning I finished up with emergency admission to hospital so missed cruise, out of hospital, a week after getting all clear fer’ the big “C”, got the bl%%dy pig flu, got over that and ended up with blood poisoning! an’t wait for this year to be over. Need to get on the water. LOL.

    @Mike Summers wrote:

    Is it me or has this Forum gone very quiet of late?

    After a forced break while I explored the pleasures of Swine Flu, finally got back to painting Kes, my MkII GRP boat (4137)

    I had already laid one coat of finish over an epoxy primer and two coats of undercoat. Rubbing down was tedious and rather disappointing as the boat went back to looking rather shabby, but today I have brought back the colour and shine (see pics).

    Which made me start to wonder…

    I have heard that a slightly matt finish is better below the water-line, something to do with micro-turbulence making the hull more slippery as the surface layer of water cannot stick to the surface of the hull.

    Any fluid dynamicists out there?

    #8688
    admin
    Member

    Well seriously big congratulations on the good bit of news hidden in your catalogue of woes. It was a brilliant windy day for sailing down here in Sussex, but not such a good day to be painting the boat…

    #8689
    Anonymous
    Inactive

    Cheers Mike. Must admit it tends to put a few things in perspective, I’ve a weeks holiday to take in November, hoping the weather Gods are kind as I might head up to the lakes for a day or twos sailing. Re’ the matt versus gloss question, I’ve no idea myself but some of the local sailors spend a lot of time polishing their hulls, some even applying a hard wax before polishing with a mop. I wish my sailing skills warranted such attention to detail, 😆 Regards, Mike. (W5316)

    #8690
    tempest51
    Member

    Hi Mike,

    According to “Boat tuning for speed” by Fred Imhoff and Lex Pranger, the ideal surface for small boats has about .005 mm granular roughness and this can be obtained by rubbing down wet with 400 grade paper. Ideally, the small surface granulations hold a thin water film which becomes almost a part of the hull and is carried along with it. Each microscopic layer of water thereafter moves slightly faster until the full water speed is reached a few millimetres out from the hull. The friction is therefore only between water and water and this is much less than water and paint.

    On a smooth but water repellant surface (waxed), air bubbles adhering to the surface cause extra turbulence which increases the already high friction between water and hull.

    Well you did ask! 🙂

    Next time you’re out swimming in shark-infested waters, rather than panic and swim off immediately, just stroke the shark a few inches back from the gills and feel how rough the texture is…maybe messrs. Imhoff and Pranger are right?

    Regards,

    Tempest51

    #8691
    Swiebertje
    Participant

    @tempest51 wrote:

    Hi Mike,

    According to “Boat tuning for speed” by Fred Imhoff and Lex Pranger,

    Well, there is a lot of debate about that theory, about the roughness of the sandpaper and also whether the hull should be sanded with longitudinal, lateral or with small circular strokes. I believe this to be relevant only for the top three boats in our fleet. IMHO us lesser deities, are better off with a smooth shiny hull to which the dirt does not stick and that saves us a lot of cleaning work during the season.

    #8705
    SeaHolly
    Member

    There must be a grain of truth in what is said by Imhoff and Pranger, otherwise the world’s top swimmers would not be wearing the newest range of sharkskin inspired suits, which were worn in more than 90% of the winnning swims at the Beijing Olympics.

    However, the sharkskin technology relies on the water flowing the right way over the “denticles” and purely having a rougher hull may not be sufficient to make that much of a difference.

    #8723
    Pete Lock
    Member

    Evening All,

    Blimey it is all getting very technical on here.

    Mike the congrats on the hull painting it is certainly looking the part. Hopefully mine will turn out similar, although the weather is going to have to be somewhat kinder to me in the spring if I am to get it ready for early summer. The weather here in Belfast has been pretty rough recently.

    Pete

    #8724

    Theoretical or practically better?

    Theoretical says rub down with 400 or 600 grade wet and dry, and leave it matt.

    Practical says: you can’t do that before every sail. You need to do it before every sali as dirt sticks so easily to a matt finish. Any speck of dirt is worse than having a nice shiny hull.
    So: wax / polish (the teflon based yachty stuff works great) and get the boat looking good – it will make you feel much happier showing the boat off, and therefore help you to sail faster.

Viewing 9 posts - 1 through 9 (of 9 total)
  • You must be logged in to reply to this topic.