Deck plugs- SA vs UK boats

Installation of instruments and electrics in the Cape Cutter 19

Postby erbster » Sat May 11, 2013 1:06 am

So you used the string in the mast to pull the cables up the mast? I was expecting to use a wire up the new hole to catch hold of the string and was wondering wether I should go up or down the mast with the wires. I'm not sure how wide the cavity is in the middle
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Postby popeye » Sat May 11, 2013 9:52 am

Hi Charles,

on page 2 of my picture Album you can see my solution but only for the masthead lights. You have to keep in mind the lower mast bolt so the distance between the socket an the mast foot has to be determined very carefully.

Kind Regards

Frank
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Postby Dennis » Sat May 11, 2013 10:21 am

erbster wrote:I'm not sure how wide the cavity is in the middle


Have a look at the bottom of the mast. The hole is the same size, top to bottom.
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CC19 Mast dimensions

Postby popeye » Sat May 11, 2013 4:52 pm

Hi,

at the boat handover bob gave me the attached drawing of the mast. The drawing shows that the HM mast has a bigger cavity than the hole in the mast foot/bottom.
But I`m´not sure if the SA masts or earlier masts (older than boat no. 106) have the same dimensions.
You should talk to Bob about this.

Kind regards,

Frank
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Postby Dennis » Sat May 11, 2013 9:09 pm

Hello Frank

The drawing you attached is very interesting.
However, I am not convinced that Mary Ann's mast #100 has been constructed in that way.

The original SA masts are hollow, constructed using the "birds mouth" technique.

I can see why HM would devise a simpler method of construction, and also why they would plan to have the hollowing in the main body of the mast, in order to get nearer to the weight of the SA masts.

However, I managed to [color="Red"]push[/color] the aerial cable for my VHF through the mast. If the mast was hollowed as the drawing suggests I think it would have "bunched up" and jammed in the widened section. I suspect that my mast at least has a 15mm x 15mm square hole only throughout the length of the mast.

This suspicion is reinforced by the weight of the mast, mine weighs 27 Kg without any fittings. :confused:

If anyone can be bothered to find the density of Douglas Fir they could calculate what the weight should be for both a solid mast and one built according to the drawing.
Cheers

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Postby erbster » Sat May 11, 2013 11:14 pm

Dennis wrote:Hello Frank

The drawing you attached is very interesting.
However, I am not convinced that Mary Ann's mast #100 has been constructed in that way.

The original SA masts are hollow, constructed using the "birds mouth" technique.

I can see why HM would devise a simpler method of construction, and also why they would plan to have the hollowing in the main body of the mast, in order to get nearer to the weight of the SA masts.

However, I managed to [color="Red"]push[/color] the aerial cable for my VHF through the mast. If the mast was hollowed as the drawing suggests I think it would have "bunched up" and jammed in the widened section. I suspect that my mast at least has a 15mm x 15mm square hole only throughout the length of the mast.

This suspicion is reinforced by the weight of the mast, mine weighs 27 Kg without any fittings. :confused:

If anyone can be bothered to find the density of Douglas Fir they could calculate what the weight should be for both a solid mast and one built according to the drawing.


Well, the figure I found (http://www.wood-database.com/lumber-identification/softwoods/douglas-fir/) was 570 kg/m3. Another source give 446 or 512, depending on where grown (http://www.csudh.edu/oliver/chemdata/woods.htm). A third gives 530 (http://www.engineeringtoolbox.com/wood-density-d_40.html). A mean value would be 514.

A very quick estimate of the mast volume (assuming its a simple solid cylinder 5.8m long with a dia 0.098m) gives a volume of 0.044m3, which suggests a mass (if solid) of 22.5kg. A square hole 5/8" (1.587cm) the whole length would remove a mass of 0.75kg, leaving a mass of less than 22kg. I don't think my mast is that light (sail no 87, Honnor built), therefore it seems likely the channel is maybe not wider for much of its length as per diag? (Though I'm not completely confident of my calculations)

To return to my earlier musings, I still haven't decided whether to pull the 5mm coax and similar dia lighting cable up or down mast. Methinks down.

Dennis was the string in place when you pushed your cable thru? What made you choose to do that rather than pull with string?
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Postby Dennis » Sun May 12, 2013 9:46 am

erbster wrote:
Dennis was the string in place when you pushed your cable thru? What made you choose to do that rather than pull with string?


Hello Charles

I cannot remember why I pushed the cable through :confused:

I just know I did. :(

I do remember pulling the cable for the nav lights through with the cord, but I cannot rermember whether that was before or after I pushed the aerial cable through!!!

BTW I agree with your calcs on the mast weight.

My mast appears to be heavier than a solid mast should be, even using the density of "green" unseasoned timber. I can only assume that it is made from a particularly dense piece of Douglas Fir.

How I envy David Peck and his carbon fibre version.

PS When you do pull your cable through the mast, remember to pull another piece of string through at the same time, that way you will still have a cord to pull in future.
Cheers

Dennis

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Postby erbster » Sun May 12, 2013 2:45 pm

Dennis wrote:Hello Charles

I cannot remember why I pushed the cable through :confused:

I just know I did. :(

How I envy David Peck and his carbon fibre version.

PS When you do pull your cable through the mast, remember to pull another piece of string through at the same time, that way you will still have a cord to pull in future.


Was planning on dragging another string thru.
The SA masts are noticeably lighter- I've done Zephyrs mast and its much easier than mine. However, I'm not sure about a carbon one- I like the look of the timber.

Thanks for all the tips chaps.

Btw. Did think about this, but decided not to for only 2 cables: http://www.saltyjohn.co.uk/cableport_boat_product.htm
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Postby Dennis » Mon May 13, 2013 10:11 am

erbster wrote: However, I'm not sure about a carbon one- I like the look of the timber.



And so do I.

Which is why I would do the same as David Peck. Have a look at the first "Whistling Rufus" album (there are four called Whistling Rufus).

No problem getting wires up (or down) that mast. :D
Cheers

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Postby Dennis » Mon May 13, 2013 11:07 am

popeye wrote:Hi,

at the boat handover bob gave me the attached drawing of the mast. The drawing shows that the HM mast has a bigger cavity than the hole in the mast foot/bottom.
But I`m´not sure if the SA masts or earlier masts (older than boat no. 106) have the same dimensions.
You should talk to Bob about this.

Kind regards,

Frank


Hello Frank

I have spoken to Bob.

The masts are solid with only a small channel for wires. They are not hollowed out as shown on the drawing.

He thinks the drawing he gave you is incorrect and is a South African drawing!

I have calculated that the volume of timber in a mast constructed according to the drawing is 35.50 litres. With an average specific gravity of 0.57, this would give a mast weight of: 20.24 Kg.

A solid mast with only a 15 x 15 mm channel would weigh 24.24 Kg.

My mast weighs 27 Kg. :eek:
Cheers

Dennis

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