View Full Version : Small Boat Mast.

07-28-2010, 04:35 PM
I would like to build a Bobcat sailboat. I'm getting a bit discouraged at the price of materials, especially the mast. I live in New England so woods like Sitka spruce and Douglas fir are expensive. I would be looking at $200.00 just for the mast. Select white pine, which is native to this area is even more. I looked at Douglas Fir framing lumber but it doesn't look like it would be a good choice or would it be "okay". Th eplans call for the mast to be 3 1/2" dia. and about 16 feet tall. The boat is a cat rig.
Thanks for any input.

07-28-2010, 04:42 PM
Most cats are a solid mast but that solid can be and really should be made from laminating smaller pieces together. That being the case...perhaps you can pick through the pile of the framing lumber for enough pieces to build the mast out of by using only the best sections of wood you can find. Scarf the pieces to length then laminate them together and shape your mast from there. Most around here would recommend you get a really nice stick of wood, cut it into slices then laminate it back together again anyway.

07-28-2010, 05:36 PM
I'd think that you could get a 16' DF 4x4 for about $5/BF or $100.
A Birdsmouth spar of 1x4 DF decking might be a bit more material.

Where are you located? Perhaps we can recommend suppliers.

07-28-2010, 05:55 PM
I built my 16' DF mast for around $60 in materials. Two reasonably clear 16' DF 2x4's epoxied together, then shaped with a power plane, beltsander and hand sander. Don't pay for the uber-high-end VG clear DF used for trim, as it costs an arm and a leg -- but if you pick through the dried DF at the better lumberyards you should be able to find something that will do.

If you can't make the needed dimensions with 2 2x4's, try a sandwich of 2x4 / 1x4 / 2x4.

07-28-2010, 07:33 PM
The local lumberyard spuce from new england makes a fine spar.
Look through the stack for a good 16 ft.-4x4 and there you go...

07-28-2010, 07:36 PM
Thanks for the feedback guys.
After reading, I think I'll give 2x6s a try. Once I rip off the round edges and bring them tot the right width I can glue the boards to the right thickness.
I live the Springfield area of Massachusetts. We still have a few privately owned lumberyards. Hopefully their wood is better quality than Homedepot.
One other question. What about Hemlock(hem fir)? It's readily available around here.

07-28-2010, 07:47 PM
I second the hollow birdsmouth idea.

You should be able to get reasonable smaller pieces of DF, scarf them to length and then use birdsmouth construction to make a nice hollow, round mast.

Your mast dimensions are almost the same as the main mast for my Kurylko Alaska. I built it, including tapers, in about 20 hours using hollow BM construction.



07-28-2010, 08:00 PM
VERY nice boat AJ.
I've been reading about the birdsmouth construction. From what I've seen I like it. Maybe I can shop around for some DF or cut up the the 2x4s or 2x6s to get pieces I need.

07-28-2010, 08:31 PM
When I was living in New Hampshire I used to get a lot of my framing lumber directly from this sawmill. They had lots of native spruce, and there was often a fair amount of relatively clear or small tight knot material mixed in with a framing package. I would recommend that you take a drive to Grantham and have a look/chitchat with these people. It's a really nice part of the country. I understand that black and white spruce is very closely comparable to Sitka, but much cheaper. There's some great brook trout fishing in the area, too. Try Dodge Brook, about 1/2 mile on the left off of Dodge Hollow Road in East Lempster. Dodge Hollow Road is east off of route 10. A very lovely part of the world, sparsely populated with friendly people. Walk about 1/4 mile upstream to the waterfall, then fish your way upstream. If you follow it far enough you will come out on route 10. I found that worms worked best there, not much room to cast a fly. Beautiful pools, clean water. In all the 8-10 years I lived and worked and fished there I never met a soul on the brook.


You might also try Ralph Balla's sawmill in South Acworth. Tell Ralph that Gil, who used to live on Tucker Road, says Hi.

This is making me want to go back there for a visit.

07-28-2010, 08:47 PM
Your local lumber yard (not the big boxes or the 'home center' where ladies go to choose among fifteen varieties of gourmet birdseed) is likely to have rough spruce 2x planks they call 'staging planks' or some rough spruce 1x8 that they call 'ledger board'. If you hunt through these piles, you might find the perfect board. If you're just starting the boat, you have lots of time to find the spar stock. When you go, bring gloves and a helper and leave the pile neater than you found it.

Never heard of anyone using 'hem-fir' for spars. DF is not actually a fir.

07-28-2010, 08:59 PM
One thing about cat boats...they were actually designed to use a solid mast...the extra weight is a benefit. I know...this is counter to all thinking but a cat is very wide and has massive stability. The extra weight aloft softens the motion of the boat so it isn't so snappy when it rides the waves. The motion is more comfortable due to the added inertia and momentum of the extra weight aloft.

wizbang 13
07-28-2010, 10:27 PM
Hemlock has very poor rot resistance ,most of it is fast growth and it kiln dries to brittle junk and it does not smell very good. Seek air dried if dealing with a local mill.

07-29-2010, 08:14 AM
Do not use HemFir. Go to your local lumberyard and ask where they keep the Black Spruce. You can get a couple 2x6s 18' long for about $20 It's stats are nearly the same as Sitka Spruce.

07-29-2010, 04:26 PM
Now I a few avenues to explore. If I make a birdsmouth mast, how many scarf joints can be in each stave.
The black spruce option sounds pretty good for about $20.00. I'll admit it, I'm pretty cheap but not at the expense of doing a good job.

07-29-2010, 06:04 PM



07-29-2010, 07:25 PM
If you do decide to use birdsmouth construction, PM me and I'll send you the spreadsheet I used to figure stave widths and thicknesses for each of the varying sections of all the spars I built on my boat (each spar is tapered)

(just realized the calculations are in the second link Thorne posted)

07-29-2010, 08:49 PM
Yabut it is much better to have someone like yourself to point this out, and to send the data directly!

07-30-2010, 07:12 AM
Black Spruce won't be any sort of short cut or compromise. I Used it for my spars for my Catspaw dinghy. Like I said, it's strength to weight ratio is nearly identical to Sitka. It works well. It's available in long clear straight lengths. I got 2 14' pieces of 2x8 with no knots, tight grain with nearly no run out in 14'. It's a good thing I bought two because I very carefully cut the first one exactly 1' too short.... It's now the support beam that I hang the dinghy from in the garage.
Yes, it took a bit of digging through the pile to find the perfect boards, but I considered that a half hour well worth the time.

07-30-2010, 07:38 AM
We were just talking about eastern white pine versus sitka spruce for paddles and small masts in another thread. I don't see any reason why eastern white pine cannot be used for a small boat mast. The mechanical bending properties of eastern white pine are within 10% of sitka spruce, and the specific gravity (i.e., weight) is very close. The mast on my Pooduck skiff is about 11 feet tall, and it is a lug rig (unsupported). My mast was built to the design dimensions for sitka spruce. I have been sailing this mast and boom of eastern white pine for nine years and there have been some heavy blows, and some accident jibes, and it is holding strong. Douglas fir is a little heavier, and stronger, but is still more expensive. Granted, the total extra cost is only going to be about twenty or thirty bucks or so, but my feeling is it is not necessary. If you wanted to be extra sure you could increase the diameter of the spar/mast so that the bending moment of inertia compensates for the 10% loss in bending strength of the white pine. It would only be a modest increase in diameter, since the greatest stresses are in the outer fibers of the mast/spar. But I don't believe that is necessary.

07-30-2010, 08:18 AM
Clear Eastern White pine is very expensive. +- $5.00bf. Construction grade Black Spruce is +- .90bf.

07-30-2010, 08:38 AM
Clear Eastern White pine is very expensive. +- $5.00bf. Construction grade Black Spruce is +- .90bf.

It depends where you buy it, I can go to my local sawmil, and find clear boards in with the common pine at $.90 bf

07-30-2010, 09:30 PM
I went to a local lumberyard today. I was pleasantly surprised. The Douglas fir didn't look too bad. There were quite a few knots but they were all tight. A 2x8x16 was less than $10.00.White pine #1 was reasonable also. So what about the knot situation. does the wood need to be totally clear or are tight knots okay.

Black Spruce isn't common here.

07-30-2010, 10:02 PM
When building the mast you want to laminate it together anyway...so you can nip out the knots and scarf your pieces together to get the best out of the material available. You didn't say whether you were going to go with Solid or Bird's Mouth though... Some small firm knots in the solid won't be a problem but they would in a BM. The mast isn't really going to need to flex...your gaff should be doing that when you need it to so small knots in the solid one are OK. OTHO...knots in the BM will be more of an issue and should be avoided as they will weaken the wall and probably cause other building issues as well.

07-31-2010, 06:31 AM
I think for my first attempt(hopefully the only attempt on this, my first boat) I'm going to make it solid. The plans have it hollowed out though.
I'll try a BM on the next sailboat I build.
I talked with my wife about building a lighthouse for the yard. The BM construction would ideal for the tapered shape and give me some practice with the construction.

07-31-2010, 08:18 AM
A lighthouse in Enfield will have to be pretty tall to attract wayward galleons full of treasure to their destruction on the rocks at Warehouse Point! ;)

07-31-2010, 10:17 AM
I have made a number of small boat masts using lumberyard 4x4's (and 6x6's).
They are 3-1/2" square, ready to layout the taper curve and cut. You will have a mast in a day.
Stay away from a "boxed heart" sticks and you will be fine, small tight knots should be a non-issue. By careful selection I have always been able to layout the waste to remove the knots.

07-31-2010, 10:58 AM
What is "Boxed Heart"

07-31-2010, 11:11 AM

07-31-2010, 11:18 AM
From the pics it appears to be the boards with the very center of the tree. Is that true?

07-31-2010, 11:28 AM
I looked at some wood pages. It appears that the boxed heart wood checks and cracks quite a bit more than non boxed heart. Not good for a mast.
Thanks for the heads up.

David G
07-31-2010, 11:44 AM
By 'boxed heart', the gentleman from Califormia means - as illustrated in the fotos - a stick which incorporates the very center (pith) of the tree. I have successfully used boxed heart sticks for spars - when the pith was centered, or very near to it, in the finished spar.

I can think of two reasons offhand to avoid boxed heart. First - warping. An off-center pith will likely end up with a stick with a wow in it somewhere. Again, centering the pith can help avoid this. Second - splitting. Boxed heart sticks tend to develop a heart check, which runs from the pith radially out to the edge. Or, sometimes, multiple smaller similar checks. This is hard to avoid, but not always catastrophic. Throughout history, there have been tons of grown spars which offered long service. If you are bothered by the split aesthetically, or worry about moisture intrusion causing rot, you can fill the crack with a mixture of rosin & beeswax. However, such a stick is NOT as strong as a completely sound spar.

But - to my mind - all of this is so much nevermind. Why? Because the plans for your boat call for a hollow mast. Now, it's true that Bolger was more of a 'concept' guy, and less of a 'detail' guy. I'd typically be less inhibited about changing/improving some of the details of his designs than with many other designers. Nonetheless, in this dept. I'd be inclined to go hollow. I'd guess that Bolger calculated that extra weight aloft would be detrimental to this boat. I am just guessing, but would want to err on the side of less weight aloft, if at all possible. Maybe you should build your test-lighthouse first?

07-31-2010, 11:54 AM
The top of the mast has a plug in it to make it solid for about 2 feet at the top.
Thanks for the info about the pith. The older I get there more I find out "I have so much to learn".

07-31-2010, 12:20 PM
The lower portion of the mast should be solid at the partners and the step as well.
So maybe the spar is hollow for ten feet? If you calculate the material removed for about ten feet at say 1-1/2" diameter the cost of making a hollow spar may not be justified.
On this little spar/boat the difference between a solid and hollow mast might amount to 1/2 or 1 foot pound of additional heeling moment.
If you were to scootch your #150 lb butt to weather just a bit that will offset it.
Now if it were a fifty foot mast, that additional heeling moment will add up and be a consideration, but on that little boat - not so much. I doubt that it was ever calculated.

07-31-2010, 12:24 PM
To be honest. it,s 195LB butt. I quess I won't have to move as far. LOL

07-31-2010, 12:46 PM
Maybe an inch...

edit to add; When you are selecting solid stock for a spar you will usually choose several that are likely candidates.
After these are scrutinized for grain run-out, ring count, proximity to the heart etc., then pick them up and weigh them in your hands. Often you will want to make the choice favoring lightness over some other esoteric cosmetic consideration.

07-31-2010, 03:55 PM
As far as ring count goes, how many to the inch should I be looking for?