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Thread: 9m Rudder to Skeg gap?(or not)

  1. #1
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    Exclamation 9m Rudder to Skeg gap?(or not)


    I noticed on the 9m the rudder to skeg arrangement seems wrong..what should the gap be (in cms)..and should rudder extend below skeg. I will have new rudders fabricated and was wondering on the best material..steel,glassfibre with core/solid, aluminium , glassed plywood etc. I presume an airfoil section would be best. I have read and noted the catalac skeg fitment problems and should the skeg extend to the transom?..Any thoughts anyone.

  2. #2
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    Default Re: 9m Rudder to Skeg gap?(or not)

    This is a common fault on Catalacs. The skeg is merely glassed onto the bottom of the hull, and was done after the hull was removed from the mould. I have seen lots with big gaps between rudder and skeg and this really impacts the effectiveness and streamlining of the system. On my boat, I added a piece of wood and then glassed over the whole in order to minimise the gap to the point that a barnacle could not get a hold!. The skeg was designed so that it was the same length as the rudder, and the bottom of the skeg has a stainless fitting which is the bottom rudder pivot. It is common for this fitting to show crevice corrossion. The fitting is also through bolted on the skeg, and it is also common for this to allow water into the skeg - which is fibreglass over a wooden centre. The skeg and the rudder are the two most common areas for a catalac to have osmosis damage. When dried out, a catalac with skegs will actually sit with significant weight on the skegs and rudders such that the rudders may not turn! This is normal!

    The strength of these skeg rudder combinations is well beyond what you will find elsewhere, however, their very strength means that they provide a lot of resistance to water flow and wetted surface.

    The Catalac (8 and 9m) also have a recessed flat point just forward of the skeg, moulded into the hull. This is the mounting point for the P bracket for the shaft drive. If you dont have a shaft drive, make sure you fare this off as well, as it is another source of underwater drag.
    Insanity is continuing to do the same thing and expecting different results

  3. #3
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    Default Re: 9m Rudder to Skeg gap?(or not)

    Hopefully the two following pictures will make things a bit clearer.

    The first is the standard fixed skeg and solid full length rudder.

    The next shows a variation of this completed by one owner, who removed the transoms completely and encapsulated new rudder posts and a canoe stern.
    Attached Images Attached Images
    Insanity is continuing to do the same thing and expecting different results

  4. #4

    Default Re: 9m Rudder to Skeg gap?(or not)

    Hi Talbot. I have just bought a Catalac 900 and the skeg on that has been moulded in the wrong place. When you say that you added a piece of wood and then glassed it in to fil the gap, you didn't say whether you added it to the rear edge of the skeg or to the leading edge of the rudder. My feeling is that it should be added to the rear edge of the skeg, would that be correct? Regards

  5. #5
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    Default Re: 9m Rudder to Skeg gap?(or not)

    Quote Originally Posted by mr maz View Post
    Hi Talbot. I have just bought a Catalac 900 and the skeg on that has been moulded in the wrong place. When you say that you added a piece of wood and then glassed it in to fil the gap, you didn't say whether you added it to the rear edge of the skeg or to the leading edge of the rudder. My feeling is that it should be added to the rear edge of the skeg, would that be correct? Regards
    On the 9m, the skeg is an add-on that was moulded on later (frequently in the wrong place!) This was because a lot of the early catalacs were based around mudeford where they were built, and had to be able to dry out. They were also built with lifting rudders.
    The 900 was built from the 9m hulls, so I expect that the skegs were also glassed on later.
    You are correct, that I added the wood to the skeg. If I recall correctly, I built it to continue the back edge of the transom as the furthest aft part of the add-on. The skeg is glass over wood, so screwing the wood to the back of the skeg is simple. I glued and screwed with epoxy to make the best job. I also used epoxy to cover the wood and fibreglass rather than gel. I was covering the hull below the waterline with VC tar anyway (rather more accepting of the occasional beaching).
    Hope this helps. Don't hesitate to ask further.
    Insanity is continuing to do the same thing and expecting different results

  6. #6

    Default Re: 9m Rudder to Skeg gap?(or not)

    Hi Talbot,
    Thanks for the info. In discussion with my surveyer, this morning, he suggests filling the gap by extending the forward edge of the rudder and then achive some degree of balancing of the rudder and thus making the steering a little lighter. I wonder what are your thoughts are of dealing with the gap in that way.
    Best regards.

  7. #7
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    Default Re: 9m Rudder to Skeg gap?(or not)

    Quote Originally Posted by mr maz View Post
    In discussion with my surveyer, this morning, he suggests filling the gap by extending the forward edge of the rudder and then achive some degree of balancing of the rudder and thus making the steering a little lighter. I wonder what are your thoughts are of dealing with the gap in that way.
    He is a surveyor so is supposed to know what he is doing, My thoughts:
    1. This would change the rudder from the original design (never a good idea unless blessed by the designer).
    2. Never heard of a balanced rudder fitted at the same time as a skeg!
    3. The forward edge of the rudder is chamfered down so it is thinner than the skeg (was on the 9m anyway). Furthermore, the edge is covered by a tape, that is not bonded terrifically well to the rudder (at least this was the case on mine).
    4. Putting it on the back of the skeg means that there is no real pressure on it. Putting it on the leading edge of the rudder would put it directly into the pressure from the propellors.
    5. Thus I would be much happier with the addition on the back of the skeg!

    But it is your call!!!!!!
    Insanity is continuing to do the same thing and expecting different results

  8. #8

    Default Re: 9m Rudder to Skeg gap?(or not)

    Hi Talbot, We really appreciate your input on this question and can see the logic of your comments. We have decided to follow your advice and extend the rear edge of the skeg, thus filling the gap. Thank you again for your thoughts and taking the time to reply. Very best regards, David (mr maz)

  9. #9
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    Default Re: 9m Rudder to Skeg gap?(or not)

    Ya'll are killing me!!! If you are so focused on that little gap betwixt the skeg and rudder, then you might want to have someone look at the gap betwixt yer ears! I'd challenge anyone to show me a difference. Sail trim, ballast, barnacles, wind, tide, waves, and staleness of yer chips will have more effect on performance than rather you fill in the gap up current or down....
    Sheesh! Just splash the vessel and sail while you have yer health....
    KNOWLEDGEABLE SENIOR CAPTAIN CHIEF OF THE EAST COAST

  10. #10
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    Default Re: 9m Rudder to Skeg gap?(or not)

    Quote Originally Posted by Capt. Terry View Post
    Ya'll are killing me!!! If you are so focused on that little gap betwixt the skeg and rudder, then you might want to have someone look at the gap betwixt yer ears! I'd challenge anyone to show me a difference. Sail trim, ballast, barnacles, wind, tide, waves, and staleness of yer chips will have more effect on performance than rather you fill in the gap up current or down....
    Sheesh! Just splash the vessel and sail while you have yer health....
    Sorry for the late response. This little gap can make a significant difference if you are planning. The large gap promotes vibration.

    The hulls were also moulded with a flat fixing plate for the P bracket for fixed shafts. If you have outboards or saildrives, it is a good idea to fill and fair over these as they create significant turbulence to the waterflow.
    Insanity is continuing to do the same thing and expecting different results

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