A bigger rudder on Coromandel Siskin

  • 14 Mar 2024 14:38
    Reply # 13329477 on 13293343

    And there it is. 

    Try to get it installed next week.

    Back in the water the 14th of April.

    I'll report on what it brings and what I lose.


    2 files
  • 23 Dec 2023 15:44
    Reply # 13294038 on 13293343
    Anonymous member (Administrator)

    Bonjour

    With the two long and flat bilge keels, the skeg and the small rudder Mingming has a tendancy to go strait ahead. It's nice when you sail offshore.

    With such a long low profile surfaces the efficiency of the rudder will anyway be limited.

    I added some camber (beheind the mast)  in the (flat) sail by using flexible battens and a double sheeting system. When I sail headwind, the helm if not firm at all but set far to windward (about 40°). It induces heavy turbulences.

    To tack, I must take some speed and inertia and then put the helm slowy almost awarship. At the end of the tack, the speed is almost to zero and the boat drifts until the speed increases to allow the keals to grip on the watter.

    Some improvements could be made :

    - add some stuff (epoxy foam for example) on the inside of the keels to provide some ort of (assymetrical) profile.

    - add endplates to the lower part of the keels but they should be sufficiently solid to support the grounding efforts.

    - add some stuff(epoxy foam for example)  to the skeg and ruder to provide some sort of profile.

    -extend the ruffer downward (balanced towards in front of the lower part of the skeg) to the level of the keel and backward to increase the rudder surface.

    - add endplates to the lower part of the rudder.

    Eric


    Last modified: 23 Dec 2023 15:49 | Anonymous member (Administrator)
  • 23 Dec 2023 11:38
    Reply # 13293992 on 13293971
    Anonymous wrote:

    @Asmat: 

    I find that moving weight forward has a lee-ing effect and balances her better than with me in the cockpit. 

    When you move your weight forward in Emmelene you find this has a luffing effect?

    Do I understand that correctly?

    And about the horizontal endplates: what size would you suggest - it seems a clever idea and I can implement it fairly easily now.

    That's mad, Antoine. You do understand me correctly, it seems that Siskin is violating the laws of physics as I understand them. 

    I converted my Kingfisher 26, Antares, from bermudan to junk rig with a cambered sail. While I was doing so, I read that another K26 JR called Chopsticks had fitted a sail with cambered panels and subsequently suffered from extremely heavy weather helm, which made her almost unmanageable unless the sail was hauled well forward. Armed with this knowledge, I fitted end plates to both the skeg and the rudder, projecting 10cm. It worked - Antares remained well balanced until the wind freshened, when dropping a panel of sail restored an easy helm, with no loss of speed.

    The attached photo, from Roger Taylor's excellent book "Voyages of a Simple Sailor" shows Mingming. Although our hulls are supposed to be identical to Corribees, it's interesting to see Coromandel skegs are quite a bit smaller, which must have an effect on steering. How difficult would it be to enlarge yours?

    Merry Christmas, 

    Asmat

    1 file
    Last modified: 23 Dec 2023 12:40 | Anonymous member
  • 23 Dec 2023 06:02
    Reply # 13293973 on 13293703
    Anonymous wrote:

    If your boat is unbalanced, is a bigger rudder the best answer? 
    surely you should aim for balance first. 
    i do recall my flat sail Coromandel was well balanced 

    The mast is fairly far aft on the boat.

    The rudder is fairly small due to the default location of the engine. I moved the engine aft as I hardly use it -: we sailed about 35 days in 2023 and sed about 5 liters of fuel. Compared to a Westerly 22 rudder it is tiny.

    The standard flat sail was somewhat better balanced than the current SJR but not much. To get the sheet to tiller arrangement going also required me to move into the cabin.

    Another sail is always on option but I must say that I am fairly pleased with the current setup and how it performs compared to the flat sail.  There are a few options to move the whole sail forward a bit and keep it there while sailing upwind. That might indeed improve balance.



    Last modified: 23 Dec 2023 09:36 | Anonymous member
  • 23 Dec 2023 05:44
    Reply # 13293971 on 13293343

    @Asmat: 

    I find that moving weight forward has a lee-ing effect and balances her better than with me in the cockpit. 

    When you move your weight forward in Emmelene you find this has a luffing effect?

    Do I understand that correctly?

    And about the horizontal endplates: what size would you suggest - it seems a clever idea and I can implement it fairly easily now.

  • 22 Dec 2023 12:01
    Reply # 13293703 on 13293343

    If your boat is unbalanced, is a bigger rudder the best answer? 
    surely you should aim for balance first. 
    i do recall my flat sail Coromandel was well balanced 

  • 21 Dec 2023 23:07
    Reply # 13293631 on 13293343

    It's strange that Siskin and Emmelène's rigs are similar, yet Siskin has heavy weather helm. I can see two aspects of Siskin's rig which may be significant: first, Siskin has less balance area ahead of the mast. The other factor may be more important - the main part of her sail seems to have a lot more camber than Emmelène's. I wouldn't be surprised if that's what is making her gripe. If the sail can be modified to flatten it, perhaps that could make the helmsman's life easier and improve performance - using the rudder to fight the rig must affect her speed.

    Antoine, I also find moving my weight forward has a major effect on trim. My boat came with a Hebridean windvane steering gear which works reasonably well, but if I move below to make a cup of tea, I find the boat stopped, pointing at the beach with her jiblets shaking. So, perhaps moving weight aft could improve Siskin's steering.

    Asmat




  • 21 Dec 2023 17:57
    Reply # 13293521 on 13293343

    Well I tried the knowledge base with only a few references. The IRA magazine issue 74 page 26 has an article on one rudder mod that adds end plates. Also issue 80 page 8 talks about a new rudder but gives no details about size or shape, just the rudder response before and after.

    However, I remember quite some discussion about rudders, both about size and end plates. So I went to the technical forum and used the google search box.

    This: looked like it might be helpful:

    Endplates

    However, it seems to have been split off from another thread and that thread is not referenced and remember much more discussion than that.

    try: General rudder endplate specs too

    Anyway, maybe try your own searches as well, my ability to form good search phrases tend not to get the best results and I am sure there are more threads that talk about rudder size, modifications and end plates.

    Also remember to search rudder balance. Making a bigger rudder, if the addition is all aft of the pivot point, may make the rudder harder to control. I have a book called "Self Steering for Sailing Craft" That I thought I downloaded from the JRA web site, but I can't find where... so maybe from somewhere else. In any case, the author does go into a lot of detail about rudder size and balance (though not end plates) as compared to keel size and rudder placement. Ah, found the link:  self steering for sailing craft

    As to the problem of end plates being a problem when drying out, I find that confusing. I would think end plates would be a plus as they allow a shorter rudder to act as if it was larger. So the bottom of the rudder should be able to remain at the same draft as the original. At the same time, if the rudder does contact the ground, the end plate would offer better support in any case (he says from his armchair). I am not familiar with this boat (even though there seem to be a lot of them around) but unless the rudder is transom hung there would only be a bottom end plate as the hull deals with the top end. On a transom hung rudder it is also worthwhile adding an upper end plate at hull draft.

    Len

  • 21 Dec 2023 12:40
    Reply # 13293370 on 13293343

    Thanx for your response.

    I sail Siskin with fairly big rudder angles (is this English?) and on a reach i find it hard to control her. I can selfsteer her on the wind with a sheet-to-tiller arrangement but only if I move my weight forward by mostly sitting in the cabin - so by moving my weight forwardt quite a bit. And in those situations I also need to use big rudder action.

    The idea would be to give her a bit more rudder surface and so less need for this big rudder action. This rudder endplate (vertical in this case) would also - I hope - make her more suited for an OGT-selfsteering installation.

    I find the idea of a horizontal trimtab / trimplate / endplate intrigueing. How would think this would work in tidal situations / estuaries, with drying out situations?


  • 21 Dec 2023 11:07
    Reply # 13293353 on 13293343
    Anonymous wrote:

    Goodmorning,

    As you may know a Coromandel has a fairly small rudder.  Many people mentioned that increasing ruddersize might be a wise thing to do when looking to increase balance while under sail. So this is one of my winter projects.

    But how much bigger is big enough and when does the rudder get too big?

    I took out the rudder this week and I am now increasing the rudder size by 12cm on the lower end of the rudderblade and 10cm on the upperside of the rudderblade. And this decision is really no more than a wild guess.

    Again: is this enough or maybe too much?

    Your input is very much appreciated!

    Best regards,

    Antoine

    That's interesting, Antoine. Why do you find Siskin needs a bigger rudder? My Emmelène is the other split junk Coromandel, (33% balance), and I find she steers easily, except that her head tends to pay off to leeward as she comes out of a tack, unless I check her.

    If I wanted to improve the rudder, I'd fit a horizontal end plate, which should be less vulnerable to damage.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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