D5 build/new member intro

[Netpackrat]

As mentioned in previous post, I ordered this black plastic mast partner "bushing" which arrived Monday. The item description was given as NAUTOS 91153 - MAST 50 MM (2") PARTNER AND PLATE - OPTIMIST but it was kind of vague as to whether the size listed referred to the outside or inside diameter. As it turns out, the O.D. is too big to fit in a 50mm or 2" hole, and the I.D. is too small for a mast of that size to fit:



So, if I want to use this part, it looks like I will need to use a mast of 1.75" diameter or just slightly less, rather than the 2" called for on the plans. But since I will be laminating the mast from 3 pieces of douglas fir, which is stronger than the called out spruce to begin with, I don't really expect this to be an issue. My reasoning behind using the plastic piece is that everything I have read about the sprit rig indicates that for best performance, the mast needs to be able to turn freely. Using a plastic bearing surface should enhance this, while also reducing wear/chafing of both the mast partner hole and the mast itself.

The only off the shelf pieces I could find are made for the Optimist dinghy, and this one seemed to be the most straighforward... One other that's available has an oblong hole, and I think I saw yet another with some sort of taper. I'm building just a general purpose dinghy, so I'm not really interested in racing tweaks. One good feature is that it included an anodized aluminum backing plate. I didn't measure the bolt holes but they appear to be sized for #10 hardware.

I'm going to post more about the other hardware I purchased before long... I guess it's going about it a little backwards, but I want to have the pieces in hand before I start building, to avoid having to make hardware related changes once I get going.

[terrulian]

That's not thinking backwards at all. It's foresight.
I've built myself into a corner by finding out at the end that my concept of hardware didn't match anything you could actually find.

[Netpackrat]

It occurred to me today, if I wanted to be super slick, I could get another one of those and bond it into the block for the mast step on the bottom. With a plastic disk in the bottom it would be an ultra low drag, low wear setup.

[Jaysen]

What are you using for a mast?

I just looked and the alum on optimist seem to be in the 1.8" od range. I think it IS right for an aluminum optimist rig but I think JM uses a standard 2" OD mast in his designs. If you don't want to use a alum mast (I was looking at dwyer) what about turning the last 4" down to 1.7"od? That will give you the rotational aspect without losing any real strength.

Just an idea.

[Netpackrat]

The plans show 2" spruce tapering down to (IIRC) 1.5" at the tip. I am going to use douglas fir laminated from 3 thinner pieces. Probably 1.75" or so tapering down to the same 1.5" at the tip, unless JM or other people more knowledgeable than I say it really needs to be 2" at the base. Doug fir is stronger than spruce for equivalent section but also heavier for equivalent strength. My feeling is that the loss of 1/4" in diameter will not be significant

I don't see there being any value to reducing it only at the base since that is the point of greatest stress. Additional thickness above the mast partner I think would only add weight.

Edit to add: If I have to stay with the 2" base I have no problem with that, and I can probably get my machinist buddy to make a similar part on his lathe. But using off the shelf parts is usually easier.

Edit 2: Assuming I calculated it anywhere close to right, based on bending strength for douglas fir vs. Sitka spruce found via Google, a 2" diameter piece of spruce would be about 7.5% stronger than a 1.75" diameter piece of fir. That's not taking into account that the fir will be laminated from multiple pieces, or that I am not going to find spruce of equal quality to the fir around here, unless I order it from an aircraft supply place. I think the 1.75" douglas fir mast will be fine.

[Netpackrat]

Picture of the stainless hardware I've bought for this so far.



I realize that the bow eye is overkill and then some, but I liked the finished look of the eye welded to the base pad, and this was the smallest one I could find like that. Moving clockwise is the set of Racelite rudder hardware... I like how one pintle is a little longer than the other, so the distance between the gudgeons doesn't have to be offset from that of the pintles as the plans suggest for easier insertion of the rudder. The little tab to the right also came with the set, but I don't know what it is supposed to do. I assume it is a retainer or stop of some sort. And at the bottom are the oarlock sockets. They take a standard 1/2" oarlock, but I am not sure yet what I am going to do for oars or oarlocks, so I will worry about that later.

Possible stupid question, keeping in mind that my total sailing experience consists of a week in Scout camp as a teenager where I earned the small boat sailing merit badge... Close to 30 years ago at this point. The plans are a little vague as to how the sheet should be rigged. Should I be planning on putting some hardware at the transom, knees, or elsewhere for the sheet?

[Jaysen]

Is the rig a sprit rig like the V series?

[Netpackrat]

Yeah, I am planning to buy the sprit sail from Bateau.

[Jaysen]

Just direct hold the sheet. Don't over complicate that until you get some time in the boat with the sail up. I say this as I was given that same advice and, as it turns out, it was right. My plan was terrible. Now that I've sailed a few times I have a better plan, but I'm going to sail a few more times before I do anything permanent.

[Netpackrat]

OK. That's what I thought the plans meant, but it seems like sitting in the middle of the dinghy it would be hard to hold a good sail shape that way. I can always add something later on if it doesn't seem to be working out. Thanks.