Jump to content


Photo

turissimo 10


  • Please log in to reply
20 replies to this topic

#1 kda

kda

    Member

  • Members
  • PipPip
  • 7 posts

Posted 06 August 2018 - 12:30 AM

hello all the wise people of Tennant land.

 

I'm a long time reader but first time poster.

I have a T10 stretched to 11m Dakota cat style i am hoping that i may be able to draw on your collective knowledge.

Except for the stern extension and a small inboard blister on the cabin the boat is built to plan.

I will probably ask lots of basic questions but i come from a dinghy background not multis. 

I believe i am suffering from excessive fore and leeward stay sag as the breeze increases and was wondering weather my rig structural set up may be causing my problems. I have a non rotating rig that has a mast base arrangement that clamps around the beam and is supported by a strut and stainless flat bar strap. I'm wondering if this is loading the main beam in funny ways and what might be done to correct this.

I'll attach some pix if I can

 

sorry for the long winded description

 

Ken

Attached Files


  • 0

#2 MarkMT

MarkMT

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 801 posts
  • LocationLake Zurich, Illinois

Posted 06 August 2018 - 06:53 AM

Others will likely have more insight into rigs on boats the size of yours, but at least in smaller boats, leeward sag would be expected upwind, yes? What makes you feel it's excessive? Downwind, what are you doing with your mainsheet? This acts as your backstay. Again I can really only speak for smaller cats but it's extremely important to have enough tension there to avoid risking the integrity of your mast. If you're relying on dinghy experience you may be letting the main out further than you should.

 

Attached File  USA233.jpg   646.26KB   0 downloads

Chris "Toothdigger" Blake and "Fast Eddie" Hansen, F16 USA233, on Lake Winnebago at Oshkosh, Wisconsin, July 13, 2014.


  • 0

#3 Vorpal Blade

Vorpal Blade

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 893 posts

Posted 06 August 2018 - 07:48 AM

Does this mast base rest on the main beam or does it sit slightly above the main beam and rely on the strap to hold it up. The latter is common practice. It could be you need to tighten the strap and use heaps more mainsheet tension. What purchase have you got? Does it go to winches? 


  • 0
for awesome custom made fabric products
http://www.coversandcanvas.co.nz

#4 kda

kda

    Member

  • Members
  • PipPip
  • 7 posts

Posted 06 August 2018 - 11:44 AM

My sagging stays are when going upwind. I'm thinking it is excessive because when sailing against boats of similar size but probably more weight as they are bridge deck boats as the breeze increases my pointing angle gets much worse as the breeze increases.

The mast base arrangement sits on the main beam with support from the strap, possibly this needs to be re-engineered back to the original design of the support post through the beam to sit above the beam with most loading on the strap. More tension on the strap may be part of the solution.

I think I have  about 8:1 purchase on the main not going to winches.

Any ideas on what sort of rig tension i should have?

My seagull striker sits vertical on the beam would angling this back towards the forestay improve its effectiveness or affect? rig tension 


  • 0

#5 MartinRF

MartinRF

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 235 posts
  • LocationStockholm, Sweden

Posted 06 August 2018 - 07:48 PM

8:1 and no winches sounds way too little to me.

http://hem.bredband....rols/index.html


 

I see no running backstays so the main sheet is what tensions the fore stay.

Are your sails of stout enough material? My first set of sails were underbuilt dacron things (1986) and de-formed badly as the wind picked up. Reefing the main was more about controling shape to be able to point rather than avoiding capsize.

 

These days I don't have this problem thanks to the wonders of modern materials. My lee shroud goes real floppy but as long as I haul in my main sheet the fore stay is OK.

 

Back to the mast base: Is there any play, anything to alow the mast to lean over? It doesn't look like it but... If not there will be some interesting loads on the mast base. Any signs of stress cracks?

 

/Martin


  • 0

#6 kda

kda

    Member

  • Members
  • PipPip
  • 7 posts

Posted 06 August 2018 - 09:04 PM

Everybody

 

Sheet tension is an idea i hadn't considered  but will certainly give more thought, could be improved without much effort. Boom vang on a dinghy does wonderful things.

 

Interesting comments about sail material. I am confident that the main is suitable for the job as it is not that old, the jib may be a bit under so could be stretching as it is loaded up, maybe a bit full for a cat as well.

 

The mast base is is set up to allow rake adjustment but nothing sideways so i'm sure it is getting loaded up in all sorts of odd ways. I'm sure i have seen some deformation whist sailing but put it down to imagination. I have crawled all over the boat looking for cracks but can find none. Looking through the mast beam i'm sure i can see a couple of marks (like a crease ) where the mast base would be but have been unable to verify with a camera, maybe to close for clear focus.

 

Any and all thoughts are greatly appreciated

 

Ken


  • 0

#7 kda

kda

    Member

  • Members
  • PipPip
  • 7 posts

Posted 11 August 2018 - 10:35 AM

would anybody have any photos (close ups) of mast bases used on Tennant style cats.

does non rotating make any difference to the loading on the mast base?

 

thanks


  • 0

#8 MartinRF

MartinRF

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 235 posts
  • LocationStockholm, Sweden

Posted 11 August 2018 - 08:26 PM

Rotating mast solution:

http://hem.bredband....hing/index.html

(scroll down to mid-page)

 

Dolphin striker for alu tube:

http://hem.bredband....hin_striker.png

 

I don't think rotating/non-rotating is important for mast base loads. Sail-mastbend interaction is another cup of tea though.

 

/Martin


  • 0

#9 Freedom GBE

Freedom GBE

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 254 posts

Posted 11 August 2018 - 09:53 PM

Nice looking Cat.

 

When the breeze comes up we crank the main on a small winch in our liitle GBE, as much as we dare to, vertical creases appear in our carbon main. Dont look at the sails, they may start to look terrible, only look at the speedo. 

 

Our dolphin striker is sleaved through the main beam and the vertical load of the mast is transferred on to the striker, there is no bend in the main beam just compression loads. It looks like yours is not like that and the main beam might bend a bit when you load it up.


  • 0

#10 ScottiE

ScottiE

    Advanced Member

  • Advanced Members
  • PipPipPip
  • 4,025 posts
  • LocationAuckland

Posted 21 August 2018 - 04:22 PM

I might have an original drawing of this in my bits and pieces at home.  Will check later


  • 0
After a decade or so of Euphoria . . . it's time to go Ballistic!
Anthony




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users