New mast top block - mounting?

[OptiMystic]

In order to go to all rope halyards, I had to get new blocks (looking at the old ones; they were due anyway). The jib is simple - pull the pin out of the old one and pin the new one in (DUH!). The mast top is a bit more complicated. I have the "standard" custom fit unit (while that sounds like an oxymoron, I think you know what I mean) that is the mast cap and block in one cast aluminum piece. The new block is just a block that needs to be mounted:



BRAND NEW dual sheave sailboat mast box block.  It requires a cutout of 3-3/4" x 5/8" and 1-3/4" of depth. It has 2 x 1-1/4" aluminum sheaves which will handle up to 3/8" line.

I really didn't think about this much up front and I obviously should have. I need to measure my mast top, but I know this block will be pretty tight. Would you cut the existing one, removing the old cast in block, fabricate an entirely new one (out of what and how?), make an adapter to suspend it over the old one or mount it some other way? I kind of lean toward the suspension route, drilling holes in the old cast top and using bushings and bolts.

EDIT - Oh yeah, I think the way I am thinking of using it may be "upside down" (not recessed) from common usage. I don't think it should pose a problem. Application is top of a 22' mast supporting a smallish mainsail (boat is my Newport 17), probably way under capacity for this block.


Thoughts?

[AdriftAtSea]

Andy-

Any photos of the mast top???

[OptiMystic]

I need to take one tonight.

This is not mine but I can use it to explain (read text below picture) :



If it doesn't show, try refresh (F5). For some reasoon I only see it half the time (?).

that is a very similar design, but disproportionate - my block/sheaves assembly is smaller compared to the mast because it is for a wire halyard. If I had one like the above, I could just replace the sheaves. Anyway, there is enough space on either side of my block to mount something for spacing on the cap and it doesn't stand up nearly as high (it's more like 1" high and probably less than 1" thick and my mast is around 4"x3" or so).

here is a picture of a Newport 17 where you can sort of make out the top of the mast:



After visiting a hardware megastore on the way in (getting stuff for something else; just browsed for ideas for this), I am thinking  aluminum square tube would make a good spacer so that the new block sits directly over the old one. I like the spacer idea for a few reasons:

• Expense, or lack thereof.
• The old block would still be there as a backup or for another use (spinaker, topping lift, lazy jacks, etc).
• Cut some square tube, drill some holes through aluminum, bolt in place. Simple; this is something I am confident I can do correctly.
• Other than the small holes I will need to drill, it is non destructive to new or existing hardware. If I find I need to go another route, I won't have boogered up anything.

Just to be clear, I am thinking of the screw holes in the new block (pic in first post) as the bottom. They would be sitting on aluminum square tubes and that assembly would straddle the current block.

Googling for images trying to find one that matched mine was very educational, BTW. I should have done that up front and will start doing that as a standard activity for barinstorming fittings.

My standard thick skin disclaimer applies - just because I seem defensive and spout justifications for my ideas doesn't mean I am not open to criticism and debate. Please pull out the long knives to carve up the idea. I am not starting on this immediately, but pretty soon.

[OptiMystic]

Here is my mast top:



I have not received the block yet to see relative size and whether or not it would straddle easily. I will post that when the block arrives.