Mainmast location for Lapwing

[Sandgroper]

Hi all,

 

I am building a Lapwing and am having trouble finding a dimension for locating the mainmast partner location.  I have a construction plan for both the Cs17 and Lapwing, and whilst the CS17 plans show the location of both the main and mizzen I can only find the mizzen location on the Lapwing plans.  Any help out ther?  Cheers, Graham

 

 

[Hirilonde]

I don't remember how I located the partner when I built mine, it was 10 years ago.  But when I hook my tape over the stem, and measure aft to the center of the partner, I get 20 1/2". The step is then located using the mast tube through the partner and the 1 in 20 ratio forward of plumb to height above step.

[Alan Stewart]

Graham, 

Thank you for bringing that to our attentions. Here is the missing dimension!

[Sandgroper]

Still on the topic of masts for Lapwing.  

 

The mizzen mast step in the plans is drawn to accommodate the 65 dia aluminium mast.  How would one accommodate the 76mm wooden mast?

 

One builder told me they put a square plug on the base of their mast and used that in the mast step.  This would stop the mast rotating, are there alternatives?

 

Thanks Graham

[Andy B]

I hope I'm not hijacking this thread ...

 

Is there anywhere a conversion chart for mast materials?  What I mean is specifications for masts in aluminum, wood, or carbon fiber for each boat?  I know the vast majority are aluminum per the plans, so I suspect not.

[Hirilonde]

I made 3" or 76mm birdsmouth wooden masts for my lapwing.  I just made the step a little bigger with a bigger hole. Just make sure you located it according to center as everything else is now different.

[Sandgroper]

Thanks Dave, my masts are already made so that was the way I was heading.  My only concern is that with the 65mm the mast step wall thickness is about 12mm, with 76mm it comes down to about 6.5mm

[Hirilonde]

It was 10 years ago, but I believe I made the block for the step bigger than in the plans to deal with the wall issue.

[Designer]

Hi Sandgroper,

 

Dave is correct, see the red lines on the drawing for the larger mast diameter. The new step will be wider than the keel batten so you need fit a piece of wood to fill in the gap.

 

This is a high stress part so you need to make it strong. The picture shows a poorly made mast step that failed. I am amazed that it lasted as long as it did. What we can learn from the picture is that there were no screws to help carry the shear loads, ply as specified has half of the grain running in the opposite direction making it harder to split and a low percentage of well bonded glue line indicating poor prep.

 

It is better to let the masts rotate so that the snotter does not tighten around the mast when you pay out the sail. On masts in tabernacles we attach the snotter snapshacle to a horizontal loop held by a pair of eyestraps. 

 

 

 

 

[Sandgroper]

Thanks Graham, the red lines helped clear things up.   I will be sure to use ply and well bonded epoxy plus screws.

 

At the risk of completely over-thinking this.  Will the mast base sit completely flush on top of the keelson, or will there be a slight gap at the forward end because the mast is raked aft?  The section across the keelson shows it flush, but if you were to draw the section lengthways would there be a gap?

[Designer]

I am glad that the drawing made sense to you. By the time I reduced the file size of the screen shot and uploaded it, the red lines are almost black on my screen.

 

Yes you are correct. Seeing that you are getting down in the weeds, you could trim the boat down by the head until the mast is vertical and pour in enough unthickened epoxy and let it level out. If you want to go a step further you make another glass tube like the main mast step, not to waterproof the mizzen step but to guide the mast into the step. I did this on Carlita, it is definitely easier to step. When thinking about it, it occurred to that if I dropped the mast in harder than I should, I might damage the the wood fibers on the keel and being hard to see or get at I laid in a layer of glass. If that pretty wood mast rotates in the thwart it will wear away the varnish, you might want to wrap a layer of glass at thwart height.

 

Glass is incredibly hard waring. After about a year of full time cruising, I wore through the oarlock rubbers and into the oar shafts on my tender. I was far from stores so I wrapped the oars in glass where needed and added turkshead stops. They were still going strong when the oars were lost 25 years later.

 

 

 

[Hirilonde]

16 hours ago, Designer said:

If that pretty wood mast rotates in the thwart it will wear away the varnish, you might want to wrap a layer of glass at thwart height.

 

I did, it works like a bushing and the mast rotates smoothly.