Damo's Sailing Boat and Tow Vehicle

[dmulally]

I ended up doing the stringers. Starting to look more boaty. 

Next will be the next two planks. Then the seat tops. Still waiting to hear from the designer about mast placement which is sort of vital and very shortly will be holding the project up. Might have to somehow research boat design. 

[dmulally]

Just working with a clever mate who knows how to steer AI with the mast calculations. It spat out a LOT of information. Most of it that doesn't make sense to me. So I'll put it here for now in an attempt to capture the salient points. 

For a 5m unstayed aluminum mast supporting approximately 10 square meters of balanced lug sail, here are the key considerations: For unstayed masts, the calculation is essentially that of a cantilevered beam, with the force acting at the height of the Center of Effort (CE) of the sail plan. The lever length is the distance from that point to where the mast emerges from the deck. For aluminum thickness and diameter calculations:

1. Looking at similar applications, a successful unstayed aluminum mast example used a 3-inch base diameter with 0.125 inch (3.175mm) wall thickness, tapering to 1-7/8 inches at the top. This was used for a sail area of approximately 105 square feet (9.75 square meters), which is very close to your 10 square meter requirement.

2. For unstayed masts, a tapered design performs better than straight tubing. A tapered flagpole-style aluminum mast provides good flexibility while maintaining strength - essentially functioning like "a poor man's carbon fiber."

3. For wooden masts, which can be adapted to aluminum with appropriate strength calculations, a common practice is to make the wall thickness about 20% of the diameter, with a taper of about 70% from base to top.

For your specific 5m mast with 10 square meter sail area, I recommend:

• Base diameter: 80-90mm (approximately 3-3.5 inches)
• Wall thickness: 3-4mm (approximately 0.125-0.156 inches)
• Top diameter: 55-60mm (approximately 2-2.4 inches)
• Material: 6082-T6 aluminum alloy (marine grade)

This should provide adequate strength while keeping weight reasonable. The taper will help distribute the bending load and improve performance while reducing weight aloft.

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Mast Calculation Process

1. Basic Parameters:

Mast height: 5m Sail area: 10 square meters Unstayed configuration (free-standing) Material: Aluminum 6082-T6 alloy

2. Force Calculation:

First, we need to estimate the maximum wind force on the sail. For sailing vessels, a standard design wind pressure is approximately 24 kg/m² (235 N/m²) for smaller craft. Wind force = Sail area × Wind pressure Wind force = 10m² × 235 N/m² = 2,350 N

3. Center of Effort (CE):

For a balanced lug rig, the center of effort is typically located at approximately 40% of the mast height above the deck. CE height = 0.4 × 5m = 2m above deck

4. Bending Moment:

The maximum bending moment occurs at the deck level and is calculated as: Bending moment = Wind force × CE height Bending moment = 2,350 N × 2m = 4,700 Nm

5. Material Properties:

For aluminum 6082-T6: Yield strength: 255 N/mm² Using a safety factor of 2 gives an allowable stress of 127.5 N/mm²

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9. Final Recommendation for Base of Mast:

Base diameter: 110mm Wall thickness: 5mm Section modulus: 41,435 mm³ (exceeds required 36,863 mm³)

For a tapered mast, we generally want about 60-70% of the base diameter at the top. With a 110mm base, the top should be around 66-77mm. For a 70% taper: Top diameter = 110mm × 0.7 = 77mm With proportional wall thickness: Top wall thickness = 5mm × 0.7 = 3.5mm Summary of Calculated Dimensions: Base diameter: 110mm (4.33 inches) Base wall thickness: 5mm (0.197 inches) Top diameter: 77mm (3.03 inches) Top wall thickness: 3.5mm (0.138 inches) Material: 6082-T6 aluminum alloy These calculations ensure the mast will have sufficient strength to handle the wind loads while maintaining a reasonable weight. The tapered design improves performance and reduces weight aloft.

 

 

 

[dmulally]

FYI this is a balanced lug yawl.

 

 

Reason being:

Unstayed mast. I don't want to spend half the morning at the boat ramp tensioning lines and setting up stays. I'll even be using a tabernacle so the mast always stays in it's housing and you just pivot it up as opposed to carrying it into a mast step and slotting it down. My back would hate that and if I were really clever I could use a winch. 

No jib. Because the lugsail is a ways in front of the mast, it doesn't lend itself to using a jib easily. More ropes deleted and don't have to faff about with a bowsprit. I can just put the anchor there instead in a roller. The small mizzen in the stern is good to help balance the boat. 

It would have been good to be able to sail with jib and mizzen in rough weather but I can always figure out a storm jib layout that doesn't require a bowsprit. That would only be in the event of having no motor and being out in stupid weather. 

And for shits and gigs. 

If the boat didn't need to be trailered and the mast would stay upright personally, I would love this sort of rig. Looks very speedy but to be honest I'm not sure it suits NZ with the silly wind gusts we get at times here. It would be forever reefed. I'll be happy with a small sail area and a larger fuel tank. 

[dmulally]

Parking this here just in case. It's for a Navigator which is a similar design but shorter and has a flat transom. For mine it will be underpowered but with where I'll be mostly sailing I'll be reefed anyway with the bullshit winds we get here. 

[dmulally]

The tabernacle is now installed and it looks like two massive paddlepop sticks. It is made from the same wood I'll make the skeg from which is a rosewood imported from Australia. Very tough wood that when painted/varnished should make quite the feature up front. I am still shopping for a mast (going through the metallurgy vs supplier process is incredibly frustrating) and have ordered some sails. 

I will add a through bolt about half way up but with the mast pivot bolted in place it should be fine. I also have it wedged against the keelson and garboard plank so it can't bend outwards without ripping a hole in the hull. I made it wide enough that it will be able to take a 6" mast although John Welsford thinks this is overkill and a 100mm mast will be ample. I'll make the back stop when I have a mast so it is supported comfortably and the rake can be set then. 

I did start playing with the transom again as I'm simply not happy with not having a motor that can lift out easily. But that can wait as I don't really need to worry about it just yet. The next activity will be the side planks and then the seat tops. Might even do some painting on the insides as when the planks go up it'll be a pain to get to some areas such as the bow. Which reminds me I need to put on the hardwood prow/nudge bar so I can get the eyelet in for the trailer winch. Doing the nuts up on that with planking and decking on will be a mission. 

Here is a pic of a tabernacle on a boat for example. 

 

 

[dmulally]

Nothing too exciting this weekend. Started on the planking which I really need to extract the digit and get done. 

It's an incredibly slow process. I make a template out of 3mm mdf then when Im happy with that I transfer it to the meranti ply and then screw and glue it on. 

I have a feeling Ill be doing this every weekend for the next month or two. Took two full days to get one plank done. I normally play on cars after work on a weekday but might need to do some more work on the boat so I can make some progress. I dont have enough time/clamps to do two planks in a day. 

[dmulally]

Got up early this morning to get the other side done. Being overcast and drizzly the temp wasn't too low so I knew the epoxy would be ok. It was only after I glued it on that I realised the front was a little too short. Thankfully it is still proud of the stem so I can cut it smooth before putting on the false stem made out of hardwood that will bash into shit. 

Now I have to let it harden for a day or so and then start the process again of shaping the stringer with a hand plane to take the next plank. Also might paint inside the bow as it's tricky to get to. 

[keltik]

17 hours ago, dmulally said:

Nothing too exciting this weekend. Started on the planking which I really need to extract the digit and get done. 

😉

[dmulally]

Boring update but perhaps could be of note for somebody building similar to see what not to do. 

Spent yesterday doing things that will be a pain in my assholes with it fully planked. Of which I'm planning to do this long weekend. 

Put in the mizzen mast step. I havent decided if I'll make a tabernacle for the mizzen or just a slot for a smaller mast. So this means I can do either down the line. 

Also put in some strengthening to the bow. As well as a doubler for any cleats up front, I wanted to link the bow stem to the mast tabernacle at the top and bottom. Adds a bit of weight but should be very rigid with hardwood lengths in there. 

 

[dmulally]

Absolutely exhausted after pulling 15 hour days for three days but finally got it planked. 

Lots of stencils are now in the incinerator drum and ready to go to hell. 

To get the stringers right it took a lot of hand planing for the planks to sit as flush as possible. The pic below shows the shavings from just the top one alone. They had to be planed for both top and bottom. If doing again I'd make the stringers wider like on the pathfinder. 

Anyway she is done now. I really should have followed the plans and done the seat tops so as to be able to fillet them from the outside but it is what it is. Ill have to do it by feel through a small locker hatch now. 

Glad it is done. Finally looking like a boat. Next on the agenda is the outboard well redesign and the false stem on the bow to make it more vikingier. 

Below left to right is more modern, heavier, powerful, reliable. 

[dmulally]

Have some big decisions to make with the cockpit layout and possible cabin. 

[rusty360]

Fark this is a cool project! I've just been searching dingy kitset projects after seeing this.

[rusty360]

Will look awesome once it's on the water.

[Stu]

Shit this is awesome! Congrats on all the hard work. Must be seventy billion hours in this.

[dmulally]

6 hours ago, Stu said:

Shit this is awesome! Congrats on all the hard work. Must be seventy billion hours in this.

Cheers mate and the others for the kind words. It's actually a nice relaxing break from fencing and rusty old car projects. I genuinely look forward to my weekends spent working on it. 

[dmulally]

Just thinking out loud and would be really keen to get some feed back on a cabin and what looks in proportion. The whaler is an open boat and for those who camp on them, they generally use a tent. Owing to the mentally unstable NZ weather I'd prefer a cabin for which I can store my bedding and stuff so I don't have to have all the lockers full of shit. A slight safety factor is that if all the lockers are full of crap, they are no longer buoyancy tanks which would be needed in case of capsize or significant leak. Plus I don't want to be tripping over tents whilst swanning about in the cabin let alone pissfarting about with erecting a tent in a storm. 

Some pictures help with what I'm mulling over and be cool to get some feedback. The official FB page is pretty cool but owing to whalers being in the minority there isn't much discussion on them. 

This is what an as per the plan whaler looks like (professionally built clearly) with the open cockpit and from what it looks like just a day sailer. 

Here is a picture of a similar Welsford design with a tent. 

Here are a couple of low cabin roofing designs which would be pretty functional to sail with and look minimal and sporty, but inside would be crawl space only and only for storage or sleeping. Not really for sitting out poor weather with a book or cooking in. 

Here is a high cabin approach which would be ok to sit up in (it is flat bottomed so unable to stand up in) and cook in. Interestingly enough this cabin is on a whaler. You can see the coaming around the cockpit is higher than a normal whaler and rises to meet the cabin at the half way mark. 

This is the interior. The flooring seen here is in place and can be 100mm lower without the floorboards and sole supports if comfortable walking on the bottom panel. 

Below are a couple of examples of a sort of mid point between crawling around like a dickhead but not having my nose rub the cabin ceiling when I sleep. Note that the coaming/cabin sides are relatively low but the roof and hatch have a more distinct curve in them to get some height. If you scroll back up to the low designs you'll see the roofs are quite flat by comparison. 

One thing to note is unlike the whaler above, I'll be making my cabin smaller and just sleeping on an angle in a V berth. So the centreboard case will be half in and half out. Which means a door can only be put in on one side of the case. Unless there was a matching door on the other side which was only just containing a cupboard for the navigation equipment and a galley rather than an actual entry point/companionway.

This is how the owner of a pathfinder got around the c/b case being in and out. With something like this which I think is pretty clever. I don't know the pathfinders well but assume the higher cockpit floor in front of the door is for where your feet go when sleeping. 

Open to any thoughts or ideas. Still not ruling out a tent. Just would prefer something more permanent. Especially as I'm only sailing by myself and possibly a dog. 

[keltik]

You're going to love a hardtop cabin you can shimmy into when it starts pissing down.  Dog will also love it for nap time

[Tiger Tamer]

Some nice boats in the above pic's. The whaler (Mistal Too) seems to be a sensible compromise, and the height of the cabin is not too high that it looks like a house boat. Interior pic's make it look usable on your knees. It's a small boat so you are never going to be able to walk around in a cabin.

I love the little black hulled boat. Looks nice with the lowish cabin. Has a rather large rudder but, must need it and could do with a longer trailer I would think.

Anyway I am impressed in how you can build a third of a boat build in the time it takes me to flare one guard on my Hillman project. It takes a lot of work plaining all the stringers and planking. Cheers

[dmulally]

Another option is a pop top although I feel that's for warmer climates where you'd want somewhere to chill out of the hot sun. 

[cubastreet]

It looks so nice open to my eyes. Would a removable cabin be an option? Kind of a ute boat.