Vagabond 20 questions for Jacques

Sail Boats 15' and up. Please include the boat type in your question.
Sarp
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Re: Vagabond 20 questions for Jacques

Post by Sarp »

Thanks for the info Jacques,

I created some cad drawings scaling the boat by 7% overall (6.5m limit) and decided to use the fixed keel. I have a few questions regarding some options;

Okoume is the original plywood, would it be ok if I switch to baltic birch? It is around 25% heavier but also a more stiff plywood. I also could not find 9mm marine grade, but there is 10mm instead. So, the bulkheads and lower chine will be 10mm instead of 9, do you think this substitution will be sufficient to support the additional weight? Do I have to scale any other panels (6 to 8mm and 12 to 15mm swap seems a bit too much)?

Can I still use 280g/m2 biaxial fiberglass or shall I swap to a heavier cloth?

Are there any other hull reinforcement I should take into account (seams, mast support pillar)?

Do I have to scale the sail area, rudder length, mast length and keel weight by 7% as well or keep them the same as in the original plans?

Sincerely,
Sarp



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Re: Vagabond 20 questions for Jacques

Post by jacquesmm »

If you scale, you must scale everything including keel, rudder and the complete rig.
For the glass, use a minimum of 400 gr/m2. That means your 280 gr biaxial plus a thin layer of woven for a total of 400gr.
Same for the seams and all fiberglass specs.

No birch please. We did some testing: birch rots easily and is weaker. Meranti or Sapele are good substitute.
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Re: Vagabond 20 questions for Jacques

Post by Sarp »

Dear Jacques,

I plan to place 2 small water tanks (50L each, regulations mandate the use of a grey water tank) one between bulkhead B/C the other between C/D on mid/starboard position. Unfortunately the C/D tank is in the way of the vertical panel coming from the cabin bunkbed lower vertical faces. Instead of having the C/D vertical plates at 34cm off-center, is it possible I install them at 51cm and use a high middle beam (10mm plywood, from bottom of hull to deck attached to the kitchen cupboard (lined 25mm to starboard side from center)?

Merry Christmas

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Re: Vagabond 20 questions for Jacques

Post by Sarp »

I found a good deal on an 8.0m mast at 74x110mm profile, 2.14kg/m. Since my hull is scaled by 7%, I was thinking about scaling the jib (both height and length) and scaling the main's length by 7%, height by 1.4% (100mm, 7.9m vs 8.0m mast). Overall sail area will be scaled by a square of 5.5% with 21.8m^2 total area. The draft of the keel will be increased by 5.5% and weight by cube of 5.5%. Is this setup suitable for my boat?

Also any insight regarding the vertical panels at bottom side kitchen cabinets?

Best Regards,
Sarp

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Re: Vagabond 20 questions for Jacques

Post by Jaysen »

Keep in mind that scaling "unevenly" will change the CoE on the sail area. This will potentially result in the CB/keel being "in the wrong spot" which will lead to some unwanted behavior. You are further complicating by changing the sail ratios as well. that changes the CoE in even more dimensions. This means that you need to rerun all the CoE calcs and ensure that you get the CB/keel AND mast in the right location now. It will be dang hard to move them once the boat is built.

If you are scaling the hull by 7% then you really really should scale EVERY DIMENSION by 7%.
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Re: Vagabond 20 questions for Jacques

Post by jacquesmm »

Keep it simple and scale everything by the same factor, for example 7%. There are sufficient safety margins built in the design when it comes to plywood thickness and fiberglass layers but it will not hurt to add a layer here and there using common sense: bottom panel, keel, mast step.

For the mast, that profile should work. The plans show the moments but the spar supplier does not. Ask him for the moments and compare. Going by what I see: size, wall thickness and weight, it looks fine, maybe a little over weight. A splice at the spreaders level is fine.

About the galley and seat, again use common sense. Scaling up by 7% will be beneficial from an ergonomic point of view. You will sit better with that 7% higher and wider bunk.

PS: thanks Jaysen. I was posting at the same time and your remarks are correct.
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Re: Vagabond 20 questions for Jacques

Post by jacquesmm »

More about the mast: I did some quick calculations and that profile looks heavy. Please stick to the moments I show on the plans, increase them a little bit if you want. I show 28 and 45 cm4, stay close to that. Most of my spar manufacturers tables show a weight of about 1.5 kg/m, 70 by 90 section with a 2 mm thickness. Your supplier (Ottomast) does not show thickness or moment of inertia . Their profile 3409 looks better.
My old Proctor mast table shows something closer to the heavy profile 3419. You choose.
If you plan to sail hard, go for the 3419, for most sailors, profile 3409 will be sufficient.
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Re: Vagabond 20 questions for Jacques

Post by Sarp »

I tried to find comparable dimensions for the mast as stated in the plans (80x120mm), shall I aim to match weight instead (1.8kg/m)?

In case I cannot add a reliable splice and the mast is at 8.0m, (1.4% increase in main height), shall I scale both the luff and foot by 1.4% or increasing luff by 1.4% and foot by 7% for both sails is fine (their area's will be scaled at the same level)?

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Re: Vagabond 20 questions for Jacques

Post by Jaysen »

The problem is that the Center of Effort (CoE) is based on the geometry of the sail. So if you only scale by 1.7% you won’t have the CoE on the sails aligned with the expected CoE the keel is resisting. The CoE will be forward on hull. This will tend to push the bow leeward.

This is why scaling really needs to adhered too.

You should be able to splice the mast. You need an interior sleeve that you peg into one section. Then you secure the sleeve in the other section once assembled.

To Jacques point, if you make the splice align with the spreaders you can leverage the spreaders mounting to secure and provide some external reinforcement.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

Sarp
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Re: Vagabond 20 questions for Jacques

Post by Sarp »

This is very valuable input for me, thank you. I knew that scaling was not recommended since it would complicate calculations, but I had to either pick this boat and scale it or another 20 feet one with a slightly higher headroom. I liked this Vagabond 20's overall design and the construction method. All in all, I need to be extra carefull so that there are no issues in terms of structure, balance & handling of the boat.

I may have to find a workshop to fabricate a mathcing sleeve to the inside of the mast. Assuming 110mm profile lenght, will a 440-500mm lenght sleeve suffice? Shall it be epoxy glued to the 2 mast parts, fastened with screws/sleeves, or welded? The spreaders are installed at 3000mm, (3210mm with 7% scale). Shall I cut the splice at slightly above this point, say 3250mm?

I still worry about the durability of a splice vs a one piece mast, but I guess CoE is more critical. The original luff and foot are 7200 / 2500 for the main and 6350 / 3300 for the jib. As an alternative to spliced mast and 7% overall scaling, If I increase the foot of both sails by 7% and their luff's by 1.4%, I think the CoE will still be at the same point on the longitudunal axis. It will be at a lower place on vertical axis compared to a full 7% scale. Would this increase the stability of the boat compard to a 7% full scale? The boat will have a lower sail performance on weak winds, but will it be noticable by an ameteur like me? (I know its a boat, but rough rule of thumb for a car's noticable performance is around 5%, anything less is usually placebo effect) Would such a setup cause any other issues to stability and handling?

Besides sails, I would like to ask about structure as well. I have scaled the entire hull by 7% in all three dimensions. The bulkheads are incresed to 10mm as it was an option in the original plans. I found 450g 45x45 biaxial fabric instead of 400 and thought it would suit well for the increased size and weight. It will be used for all structural seams as well as covering the bottom + chines from bottom side. Here is an area that wasn't clear for me in the plans. The topsides&decksides have an option of using 6mm plywood with biaxial fabric on both saides, but from the drawings I can only see a bottom covering for the 12mm bottom and 8mm chine plates. Shall I use the 450g fabric to cover both sides of these bottom and chine frames or just the bottom side? (Is the inside of the cabin just seams on edges and epoxy on the rest of the surfaces?) I will use the 300g biaxial to cover 6mm decksides, 6mm topsides and 8mm deck from again both sides? Do I need to increase the fabric to 350g/m2?

I'm planning to enlarge the mast support pillar from 50x25 to 60x30 while the deck support stringers will be 28x30 and 20x80 middle (I could not find 25x30 or 15x75). All of the seating surfaces and vertical panels both inside and outside are also 10mm (8mm marine okoume was not available at the larger size to cover the seating surfaces for cabin/cockpit with minimal plywood waste and I used the inside of the bulkhead frames as well) Do you see any issues with the hull structure?

Thank you for your help

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