Is my boat safe?

Discussion in 'Stability' started by RoyalStar, Jan 14, 2008.

  1. RoyalStar
    Joined: Jan 2008
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    RoyalStar Junior Member

    Hi

    Is it possible to tell me if my trailer sailer yacht has adequate stability if I provide the dimensions? I find the boat to be very tender - and I am aware that some of these boats have capsized and some sunk. I wish to use it for coastal sailing in fair conditions.

    I am also aware that since the boat was built it has had a few additions: Roller reefing foresail, backstay and mast crane, outboard mounting on transom and outboard, mast tabernackle.

    It is of GRP construction.
    Overall length 16'3" (4.95m)
    Waterline length 14'2" (4.32m)
    Beam 6'3" (1.91m)
    Draft (plate down) 2'6" (0.75m)
    Sail area 120 sq ft (11.2m)
    Mast 20'6" (6.25m)
    Total weight 750lbs (340kg)
    The boat has a mild steel centreplate that fully retracts. The centreplate weighs 90lbs (41kg). There is also fixed ballast in the bow of 75lbs (34kg).


    Thanks for any help and suggestions you can give me.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    This information is helpful, but much could be saved if you provided the year, model and manufacture. Stability calculations can be complicated and drawn out, as there are a number of variables.

    My next question is of your sailing experience in lightly ballasted or unballasted boats. Capsizes are typically the result of skipper/crew error (getting caught with your pants down or bad habbits) and should be taken with a grain of salt, possibly the whole salt shaker.

    What angles of heel are you experiencing in 10 knots of wind with a crew of two (avarage size people)? 15 knots?

    Lastly, pictures of the general shape of the hull, both profile and sectional, if you don't have drawings of the old gal, would be a tremendous help in accessing how firm her bilges are, amount of lateral area, etc.

    By the numbers provided, she doesn't seem particularly out of the ordinary, except in board down draft, which appears low. Her low 20's ballast/displacement ratio is often typical of small centerboarders and not a concern, unless she's especially slack bilged and/or on a narrow WL beam. Her SA/D seems reasonable, certainly not a sparkling light air performer, so not easily over pressed.
     
  3. RoyalStar
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    RoyalStar Junior Member

    Hi Par

    Thanks for your thoughts. I've attached some photos that might help with the points you queried.

    I'm afraid that I can't accurately tell you what angles of heel I am getting. My partner and I are both ex dinghy sailers and are fairly convinced that this is what stopped us going over this summer when rapid movement of the crew to the high side and me releasing the main sheet stopped the boat heeling when the rail was at the water. This was when we had been sailing happily in approx 10mph of wind and a gust of 15mph hit us. I would guess that when the rail hits the water on this design heel is approaching 45 degrees. What worried me was there no sensation of the boat rounding up or having reached an angle at which further heeling was restricted. (Some boats seem to me to quite quickly heel to say fifteen degrees and then they are quite stiff.)

    Any further thoughts of yours would be most appreciated.

    I had considered fitting the mainsail from a popular dinghy that has the same area but is approx 1 metre shorter (lower aspect ratio) to lower the centre of effort. I could then lop the top of the mast - lowering the cg. Would this be a bad idea?
    I had also considered epoxying some concrete bricks into the inside bottom of the boat next to the cenreboard casing to offset the weight of the items added since manufacture. But I'm not sure how to work out how much to add as I am unsure where to calculate the moment arm from.

    Cheers
     

    Attached Files:

  4. Pericles
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    Pericles Senior Member

  5. RoyalStar
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    RoyalStar Junior Member

    Wow - what fantastic looking boats!

    And I can't believe the sail area!!!


    But looking further - I found this snippet:
    Do Sandbaggers Flip?


    Ever wonder if a Sandbagger like Bull & Bear could flip over? THe answer is YES!!! They have many a time, but are sealed boats now and only take a moment to tip back upright.


    My boat is definitely not sealed - and has no built in buoyancy. So sinking is a real possibility.
    But I will talk to my partner about hauling bags of gravel from side to side.
    Cheers
     
  6. Pericles
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    Pericles Senior Member

  7. RoyalStar
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    RoyalStar Junior Member

    Excellent plan. Yes - makes perfect sense to do some easy experimenting before committing.


    But... how will I know when I have got it 'right'? Do I just keep adding weight in the bottom until we stop getting scary moments?

    Or is there some system based on PAR's 'angle of heel in 10mph wind' question. The boat designer said the angle of heel should be kept to 15 to 20 degrees (and if that angle is to be exceeded for anything other than a brief squall sail then should be reduced.) So maybe I should add ballast until I get less than 20 degrees of heel with all the sails up in 10mph of wind?

    Cheers
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Your boat, using the numbers you've provided suggests a D/L of 118, which makes her a light weight, though not ridiculously so. Her Capsize screen is 2.75 and suggests she'll surely capsize, if not handled properly. The point of vanishing stability looks to be in the 115 degree range, meaning she'll likely survive a knock down, be relatively slow to get back up, particularly if partly swamped.

    My impressions of the images are a couple of dinghy sailors that have had their taste of a round bellied boat and dearly miss the high initial stability of their dinghies.

    This hull appears to require around 17-20 degrees of heel to get in the groove. For a dinghy sailor, this is holy grail territory, because you've been sailing with heel angles 10 degrees and less.

    Her tall cabin sides, heavy roof crown and well outboard comings suggest this is the case, she needs to be sailed on her ear, probably with her rails down or very near so. Her SA/D is sort of high at 23, meaning her light air performance should be good and that she can be over powered in gusts, but hey, you dinghy sailors live for this right?

    Personally I'd do a heeling test and a capsize test and see exactly how bad it is or if my suggestion of a couple of dinghy sailors being out of their element is warranted. I'll bet you can lay her on her beams ends, then let her go and she'll pop right back up.

    Take her out in 10 knot winds with gusts to 15 and bring a "incline-o-meter" with you. Try different sheet and hiking locations and get her in the groove, then check the angle of heel. How close was the rail at the best speed, etc. In those wind strengths, you'll probably be in the low to mid teens as far as heel angle. A heavy gust may push you to 20 for a moment.
     
  9. Pericles
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    Pericles Senior Member

    PAR is your man.

    Pericles
     
  10. RoyalStar
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    RoyalStar Junior Member

    Hi PAR

    Thanks ever so much for your time and thoughts.

    I think that there is much in what you say about two dinghy sailers out of their comfort zone. That said - and I'm not sure how it relates - we spent two weeks in the Greek Islands in the summer sailing a Beneteau 305 that seemed rock steady with its rail on the water. It was when we got back in our own little boat after that that we scared ourselves.

    Given what you said in your first paragraph, should I be happily setting off to sea knowing that the boat has no positive buoyancy? Put another way - would you expect it to meet modern certification standards for coastal use?

    I think the two tests you recommend are what I must do. But how do I do a capsize test that doesn't have result a = safe: result b = boat at bottom of lake/sea? (Is there a 'standard' capsize test - mast top touching water?) I suppose doing it in tidal shallows would have the benefit of the wreckage being available at low water... but there must be better ways??


    Notwithstanding all of the above, and lets say the tests pan out as you expect or even better. Is there anything sensible I could do to make the boat feel stiffer.
    Would simply adding lead in the bottom of the boat stiffen her up and move me out of the 'she'll surely capsize, if not handled properly' zone?

    • Would a lower aspect ratio main sail make any actual difference?

    Its one thing being relaxed about capsizes and knock downs in a dinghy with a rescue boat a few yards away, a boat you know will float and that you can easily right, and a warm clubhouse ten minutes away. But I intend making full day coastal passages where rescue will mean a lifeboat or a helicopter looking for heads in lifejackets - assuming the flares and the radio didn't go down with the boat....

    Maybe my priority should simply be ensuring that the boat has positive buoyancy. Once I know it will stay afloat then a capsize becomes an emergency situation - rather than quite possibly game over.

    Any further thoughts most appreciated.

    Cheers
     
  11. PAR
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    PAR Yacht Designer/Builder

    That Beneteau 305 is a 30' boat weighing 10 times as much. The difference would feel like stepping from a ocean liner onto a lifeboat.

    You're going to have to trust the boat, which currently you don't and it's an easy stretch for a dinghy sailor to get into. This little boat you have is what I would call "lively" and fun to sail, once you get to know the old gal.

    Sailing that Beneteau 305 really screwed up your senses. You sailed a fat butted, high ballast ratio yacht and the sensations are very different then the little boat you have on your nerves.

    I recommend you see what the real heel angles are. Mostly you have to put time in the boat, which will build confidence. I'll bet you can sail her way over (remember her SA/D is 23+) and she'll just rock and roll with the puffs.

    With 115 degrees of positive righting arm, you'll have to stuff the mast well under the water in capsize, to get her to go turtle on you. It's unlikely you'll get blown down more then 95 degrees, so you'll be okay. Of course you'll be trying your best to leave the boat, long before you get to these heel angles and some down flooding will be happening. Once those huge cabin sides hit the water, the stability curve will flatten out a bunch, providing a fancy reserve. I don't think it can remain on its side, but will pop back up.

    Yes, there are tests, yes, you can cut the rig or toss ballast in her, though the centers will likely move and you'll have balance issues.

    Sail the boat, in light winds, reef early when you get nervous and get accurate heel angle readings so you can redeem your self-esteem, once you realize that 15 degrees feels like 40 to a dinghy sailor.
     
  12. alan white
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    alan white Senior Member

    While technical information is helpful, the boat looks reasonably seaworthy. a similar boat, the West Wight Potter, has crossed the Atlantic ocean.
    Safety is not only about ballast ratios and sail/displacement ratios, but just as importantly about construction, rigging/sail quality, flotation, cabin hatch scantlings, and so forth.
    It is important, I think, to develop a visual feel for each part of your boat. Seaworthy and safe operation depend on a lot of things working well under stress, including the sailor himself.
    Look at the fittings like the cleats, blocks, and tangs closely. Look at the method by which the deck was joined to the hull. Look at the lines, both standing and running. Are they beefy enough?
    Calculate and see if your flotation is enough to keep the boat afloat.
    How is it equipped? Does it have a good anchor/rode, bucket, bilge pump, air horn, whistle, lighting, VHF, and so forth?
    Every boat I've owned, I've found certain things done wrong, poorly attached, undersized, worn, missing, or of such crummy quality that they begged to be replaced immediately.
    Three things make a safe boat; a concerned and informed sailor, a sound and well built boat, and an experience of sailor and boat together for a length of time.
    It's likely you could confidently sail just about anywhere if you can manage to achieve those three items. Whether your current boat is worth improving (and you'll find that no boat needs NO improvement), only you will discover over time. You have to get to know a boat real well. When you have turned every screw, removed and reattached or replaced every fitting, seen past the surfaces into the structure itself and made it right if it isn't up to par (no pun), you will feel a solid confidence in your boat and you will trust it to take you where you want to go.
    Having been through that process a few times (always buying fixer-uppers to get the boat I wanted), I can tell you a lot of boats out there are barely afloat, and held together with God knows what---- and they are not safe boats at all, no matter how much safety was designed into them by the architect.

    Alan
     

  13. RoyalStar
    Joined: Jan 2008
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    RoyalStar Junior Member

    Thanks PAR - I think you have nailed the situation precisely. I will get an inclinometer - and (come summer) get some serious time in on her.

    Thanks also to Alan. Good points. I shall invest my time and effort between now and the start of the season into making sure the hatches fasten properly and installing flotation.

    Cheers
     
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