Majorly Modifying SJ-35

Discussion in 'Boat Design' started by Peter Quinn, Sep 28, 2011.

  1. Peter Quinn
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    Peter Quinn Peter Quinn

    I am the proud owner of an Oyster SJ-35 mod. The keel was modified in 1988 with a Steven Jones designed keel bulb (I am told it is the bulb design that became standard on many SJ designs in 1989), and the IOR pinch was partially filled in to aid handling and flow.
    FLYER has a great race history on the Great Lakes and is now on the Chesapeake. As she sits at the pier, she looks to be 2-3 deg bow down trim, when the boat is race light, she wants to plow a bit. (This was not the case when she was loaded for delivery sailing offshore in 15ft waves. I understand this is a boat trim issue, but it also seems to be a form issue.)
    My desire is two fold.
    1. I would like to increase downwind/high surf sea keeping.
    2. I would like to make her competitive against the modern hulls

    My initial thought is to follow the lead of the west coast former IOR PENDRAGON II, which was modified by Bravura Yachts Inc - The Refit of the Pendragon II by Leif Beiley
    www.bravurayachts.com/pendragon_refit.htm

    PENDRAGONII received a new keel, bow and rudder.

    I think FLYER would benefit from a new bow and rudder. Ideally, I would switch the keel to a modern blade and bulb.

    I am a naval architect by schooling, however, do not work professionally in the field. I would like to make an attempt at designing the mods myself, however, I have yet been able to acquire the original lines.

    I am open to thoughts, lessons learned, etc.
     
  2. upchurchmr
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    upchurchmr Senior Member

    You might want to check this thread, since you do not have the lines to start from.

    http://www.boatdesign.net/forums/boat-design/had-my-old-boat-scanned-39889.html

    When we have a CG problem with a fighter jet, we just add ballast as far aft (in your case) as possible. Perhaps the next thing would be to move the keel/ bulb aft to get the waterline you want.

    Bow, Keel, and rudder seems like a lot of make work unless you want to compete at the top of the heap. (Possibly somebody made lot of money off of an anxious owner).

    At least with the scanning above you will have something to start with.

    Marc
     
  3. michael pierzga
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    michael pierzga Senior Member

    The pendragon modification looks sensible...and expensive. Is it worth the effort ?
     
  4. Peter Quinn
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    Peter Quinn Peter Quinn

    Yes, PendragonII was reported to be an expensive mod. FLYER's race history is very well established on the Great Lakes, with 23 MAC races, claiming 5 class wins. She has been sailed very well in her current configuration. My concerns are more an issue of downwind seakeeping, and making her smoother through waves to keep momentum. I already incur a "modification penalty of 6 sec. However, she really does not sail to that penalty. The rudder is 1988 carbon technology and foil shape. Second the "bulb" keel is really a fin keel with external lead bolted and faired. I could probably fix the trim issue with simply removing the rest of the skeg and shifting internal weight. If I tackle the skep though, there is little reason to keep the same rudder. Going to a longer modern blade would help ease that 6 sec penalty.
    The bow mod would allow me to go to a bowsprit and masthead asym. Without increase volume forward, I do not believe the bow be able to safely handle the extra sail and forward center of effort.
    As far as adding ballast aft - I do not want to increase the Lwl to displacement ratio it is already 193. More importantly, the under water shape creates a forward force under dynamic forces - much like an airplane trims out nose down at its higher speed limits (ie T-2 Buckeye).

    If I can find a used modern bulb keel, I would happily start with the keel. The work aft, leaving the new bow as a future option.

    Thank you for the thread on the scanning. I will look into it further.

    What I am really trying to determine now is whether or not a modern bulb keel presents any problems or negative performance issues when retrofitting it to an IOR hull.

    I am also willing to take on most of these mods by myself.
     
  5. upchurchmr
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    upchurchmr Senior Member

    I cannot help with the IOR related questions, never been remotely a part of that.

    Good Luck
     
  6. Chuck Losness
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    Chuck Losness Senior Member

    Peter
    I was actively racing (not my own boat but as crew) in So Cal when PendragonII was modified. The modifications definitely made it a faster boat. But I don't remember it really doing that well racing after the mod's were made. I think that the rating penalties were just too great to over come. PHRF just doesn't like modified boats. One thing to be careful of is that visually the bow had a pinched in look to it. Might have been just an optical illusion but you could tell at a glance that the bow had been altered.
    You might contact Eric Sponberg. He did a similar modification to a Freedom 39 and has an article on his website.
     
  7. Peter Quinn
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    Peter Quinn Peter Quinn

    Chuck,
    Thank you. I had already researched WOBEGONE DAZE and think the lines look really good. I would like to avoid using wood anywhere. I saw the "pinch" bow on Pendragon. It seems to be very slight and only visible in a few photos. I currently have two penalties for FLYER- 6 sec for carrying Asym and Sym spinnakers, and 6 sec for the mods. Moding the bow would change the waterline, but I think I could get the other mods in under the current penalty.
    Option 2: cut out the 7ft of skeg and fair the aft section. this would remove approximately the same volume that was added to fill the pinch. Then I could change could upgrade the rudder. Option 2 should not affect my current rating as I am already penalized for these.
     
  8. Mike Dennehy
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    Mike Dennehy New Member

    Peter,
    Also the proud owner of an SJ35 in the UK, which my boat partner and I recently spent a couple of years rebuilding / refurbishing.
    One of the points we addressed was the original IOR tendency to be little bow-down, which could result in rudder losing grip, and therefore needed an early reef. Some owners fix it with plenty of lead under the companionway to move the CoG aft. We also did not like the mid-saloon position for the engine over the keel, and so fixed both issues at the same time.
    After a discussion with Stephen Jones the designer, we re-engined her with a sail-drive placed on a new engine bed aft under the companionway. His advice was 'the best modification you could make'.
    Result = 1) space for a more useable table in the saloon.
    2) less vibration as no prop shaft / p-bracket.
    3) lose the lead ballast.
    4) very happy owners with as-yet no nasty broaches.

    As an alternative solution, in the late 1980's four SJ35's had their keel recast to an elliptical shape which also resulted in a movement of weight aft.
    No plans for us to do that yet.

    This link contains details of a few SJ35's, including another which recently had a bulb added the bottom of the keel.
    http://www.sailingnetworks.com/boats/view/5543

    Hope you find it of interest
     
  9. Peter Quinn
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    Peter Quinn Peter Quinn

    Mike,
    Thank you for that info! I have been considering the engine move for the same reasons. Did you have to reinforce the hull under the ladder? I am interested in photos of the interior if you have any.
    The engine mod would help reduce drag and help the CG. FLYER, however, also has her IOR pinch fair in. This added several hundred pounds of buoyancy to just aft of the prop. So she has an even greater tendency to dive the bow.
    FLYER was one of the first to receive a "bulb" keel mod. It is really a partial bulb added to the original fin keel. Highly recommend this mod! Really helps with stabilizing the IOR hull.
    May I ask how you got in contact with Stephan Jones? I have attempt twice without success.
     
  10. Peter Quinn
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    Peter Quinn Peter Quinn

    Mike,
    I like the "teak" decking on the cockpit seat! I think I will follow your lead.
     
  11. Mike Dennehy
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    Mike Dennehy New Member

    Peter,
    Apologies for radio silence. Been away on vacation.
    Regarding a contact for Stephen Jones, I'm not sure of the protocols for giving out his personal email address. But you should be able to locate SJYacht Designs on the web.

    Here is the text of my question and his reply.

    Dear Mr Jones,
    I have recently purchased 'Erotic Bear' an SJ35 with which you doubtless are familiar, and intend to use her for a combination of racing and cruising.
    There are a couple of topics about which I would appreciate your guidance:

    1. Weight Distribution.
    I understand that several owners find benefit in adding some weight behind the CoG, partly driven by the different rules for IOR / IRC.
    'Erotic Bear' has the original keel, and I know that a small number of boats replaced this with the elliptical version.
    It was not my intention to replace the keel.
    However... In placing internal ballast aft, can you offer some guidance about:
    - the optimal amount.
    - its best location.
    - if the hull is likely to need strengthening at that point.


    2. Saildrive possibilities.
    'Erotic Bear' is fitted with a Yanmar 2GM (most likely the original) and the standard prop-shaft arrangement.
    Do you know if any other SJ35 has been converted to use a saildrive?
    What is your view on the merits of such a conversion?
    I was wondering if in addition to the more usual benefits of noise / vibration, this might also bring a benefit in terms of weight distribution?
    How far aft do you think it would be sensible to site the engine?
    For instance, do you think it would be OK in the vicinity of the companionway?
    Do you foresee problems with the additional stiffening necessary?
    Would this location make her too stern-heavy?
    Would compensating internal ballast over the keel be necessary?

    Any thoughts you have would be much appreciated.

    Regards

    Mike Dennehy


    Dear Mr. Dennehy,
    On weight distribution sail drives and ballast the overall answer is yes to everything.

    Saildrive good, and the bonding-in of the grp 'pod' is its own stiffening.
    Place new motor in traditional place under companionway with any additional ballast just in front of this location.
    I think if memory serves that Erotic Bear shared the slightly heavier keel enjoyed also by Richard Matthews' Oystercatcher(the first of the class) but I can't be certain.
    If so she will be a little stiffer than others of the class who used to benefit from the addition of about 300lbs of internal ballast to give them more 'gravitas' upwind.
    It may be worth trying her without to see as the addition of extra ballast can be easily done afloat.
    Make sure this is reported as it should lower the rating.
    In any event the flotation overhangs etc. will need reassessing with the new engine location.
    IOR stern designs are generally 'light' and in case of SJ 35 certainly would benefit from more immersion.
    Hope this is helpfull.
    Yours sincerely,

    Stephen Jones


    So that's what we did!
    I will shortly send another mail with more details, and attempt to add some pics.
    Mike
     

  12. Peter Quinn
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    Peter Quinn Peter Quinn

    Mike thanks for the input. I definitely think moving the engine and installing a saildrive is step 1.
     
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