My Design - Trifoglio 25' - Suggestions & Opinions

Dear All,
this is my first post here. I am an avid reader, and I want to thank you all for the great insights found. I studied many threads, and some of them have been printed, and found their place in the Yacht Design Books shelf.
To make a long story short. I am a 46y.o. man, and I love boats, anything that floats actually, especially sailing ones. Like many before me, I am trying to design my own boat, which I hope, sooner of (sigh) later to build. I love scow bows and junk rigs, and that's what I went for.
I tried to design an internal ballast with leeboards, which I love, but it did not work out. I guess it is easier to design something similar to what you are used to see, and where I sail - Liguria, Italy - draft is not an issue. I therefore switched to a scow bowed hull with fin keel, which is also an idea I like very much. What I would like to understand better, is how to design the join between hull and keel. I have read many post about this topic here (thanks PAR) but I still need some (many..) suggestions.
Is the keel bolted to the hull (so the upper part of the keel need to have a curved shape to adhere to the hull), or to an external thing, added below the hull with an easier flat surface?
Any other kind of opinion or suggestion is very welcome.

Please be kind: she is the product of many sleepless nights..


DVV

 

Welcome DVV,
Your lines are certainly pretty. I would love to see more pictures from different angles of her. I am also interested in reading more about the design choices you've made, especially what you like about the scow.

To give you an idea of where my thinking comes from on your question, I'm an artist who loves to sail and has some experience growing up around boats and boat builders, but I am not a designer and have never built a boat myself. So, in that spirit, take my advice only after thoroughly researching and coming to a better educated conclusion.

As for attaching a fin keel, your construction methods will have some say in how you choose to attach the keel.

Thinking in terms of wood construction, and sizes in the range of 10 meters or less, curving the married surface to the hull might be easier to build. Larger scales may be harder to get the shapes to match up and attaching the keel to a faired stub keel might be easier.

With glass construction, I would think you could go either way. You could also lay up the keel and hull together as one piece.

-Will (Dragonfly)

 

First of all thank you for your reply.

The idea was to design something to be homebuilt, with the lower possible budget (I guess this is quite a standard..). It is supposed to be epoxied plywood. I bought building plans for Michalik Piccup Pram, which should have been built last summer. I really love the Piccup, and you can see the resemblance in the bow shape and in what Jim calls the - absence of - shoulders. In the internal ballasted version I had much more rocker and I also tried a box shaped (one chine) version, to use form stability a bit more.
When trying to evaluate the cost of building the Piccup, I soon realized that amateur boat building is an expensive hobby, which does not fit easily to my pockets. So I had to decide to skip the 'training building', and focus directly to my main focus: a 7,5 meter sailboat. I wont have the possibility - read: money - to play around, if I can do one build, that will be it.
So, I wanted her to be 25 feet. Scow bowed. Junk rigged.
- 25 feet: I've always loved this size, enough to be a boat in which to travel, not enough to be impossible to design and built;
- Scow Bowed: to me, its just better. Mainly for the effect this have on the waterlines. They are more balanced and straight than a traditional pointy bow. 'Water does not like to be surprised'. I cant remember who said it, but this is one of my top of the list design priority. Is such a bow slower upwind with low winds and a chop, as they say?! I dont know. May be. But I cant see it if a think of a heeled vessel, and anyway anything has its limitations;
- Junk Rigged: for two reasons, it is the easiest and cheapest way to rig a boat, you can use a street light pole (like Mingming), and you can build sail yourself. The second reason is because I love the easy reefing ability, which also allows for an internal control station, with a whipstaff tiller and a Jester style pram. I love sailing in wintertimes, and I like the idea of being able to stay inside and warm, when its too cold outside.

 

Google Triloboat "great auk"

 

DVV, you might find some interesting ideas in Glory, as shown in the attached article from Practical Boat Owner 20 years ago.

OK, she is not a scow, but she has a very neat junk rig. Her hull is a standard 19'6" Colvic Watson design which Henry bought as a bare shell, and then he built the rest himself.
He has been around the world with her, in addition to sailing from the UK to San Francisco and back (both times via Panama), and in his later years summer cruises every year from the south coast of England up to the Shetland Islands (north of Scotland) to visit his daughter (who lived up there).

Re your proposed keel attachment - I think the easiest would be if you have a stub keel built into the boat, which you then attach the ballast keel to with sturdy through bolts.

 

Thank you
I know Triloboats but I passed through 'great auk' quickly. I will have a deeper look, but I gave up the idea of a boat wo keel.
The initial idea was to have leeboards and internal ballast, but I did not feel comfortable in designing a hull that was adapt.
This is my first design, and the design went in the direction of hull shapes which I have seen and sailed on. I guess its normal, I sail mainly in Northern Italy, near France, in areas in which there are not much leeboard boats.

 

I like very much Glory, she was one of the boats that made me love so much the junk rig. There are many interesting ideas, but I'm afraid me and Sir Piggot started with a different budget in mind.
One of my main drivers in the design process, was to design something I could build for real. As simple and low cost as I was able to design her. Adding a keel was something I had to do, in order to make it work, and this will increase the expenses quite a bit. I want a boat that can be used also from outside, and I think a Jester style pram-hood from which you can reach all the lines will be enough.

Talking about Keels. You suggestion is interesting, I was wondering about pictures of SibLim (you can find more details about this interesting project in the junk rig association forum) which has a stub keel attachment. Three are the solutions I am thinking about, and all the doubts that I have:
- Keel with a curved upper surface to marry the hull: how much does is cost to have it made? Can I build it myself with a shape like that? Can I homebuild a 6/700 kg hull?!?!
- Stub Keel and keel attached to that: would it be difficult to build? Would it be difficult to design (read: to make the software (Freeship!+) understand what I want and do the stability calculations properly)? Agan, can I homebuild it? How much would it cost to have it made?
- Incapsulated Keel: if my understanding is correct, this would mean build a keel out of wood (plywood or other kind of wood?) empty inside, fill it with lead spheres (I would use small lead spheres because I can have them from a friend at a friendly price), and then epoxy and attach keel to hull. How do I calculate the weight of the lead before actually doing it? Would I be able to design it and make the calculations?

Thank you for your post, if you have any other idea and/or suggestion please let me know?

DVV

 

Update: I think I will try the encapsulated keel solution: it seems the easiest and cheapest way to do it.
I can fill it with lead spheres. I found out that the packing density (this is how they call it) of randomly packed spheres is 64% of concrete.
I just have to find out the weight of the mix 64% lead 36% epoxy to obtain the correct dimension.

Anyone here does know which is the epoxy weight? I will google it, guess its not difficult to find out

 

The density of lead is 11,343 kg / cubic metre - if you mix small lead spheres with epoxy I am sure that the proportion by volume of the lead is going to be considerably more than 64%.
Density of Metals - The Engineering Mindset https://theengineeringmindset.com/density-of-metals/
You could carry out a simple experiment with some lead spheres in (for example) a 500 milli-litre container to find out what this percentage actually is.
Fill the container with lead to the brim, and then weigh it. Now add water to the container until the water level is at the brim (or at the 500 ml mark) and weigh it again. The difference will be the weight of the water that you have added. Liquid epoxy should behave in a similar fashion to the water, in that there should be very few air voids if it is all mixed well.

 

I made the same guess, but it looks to be wrong.
''For equal spheres in three dimensions, the densest packing uses approximately 74% of the volume. A random packing of equal spheres generally has a density around 64%.''
This is from wikipedia, but I searched a lot and all confirms this. Moreover - strange to accept at the beginning, but obviously true after you figure it out - this density does not depend on the sphere radius (within an acceptable range). I found many Academic Papers on this subject, this is a hot topic for the logistic industry.

Higher values (up to 93%) would be obtained using sphere of different dimensions. I read that encapsulated keels are usually filled with lead bars, and the space in between filled with small spheres and then epoxy. That would be a nightmare to estimate, but may be I'll give it a try...

 

What is the diameter of the spheres that you are planning on using? The smaller the diameter, the denser will be the packing.
I am sure that if you filled a glass with lead shot (eg from a pellet gun), and then filled it with water, you should achieve a density greater than 74%?
The easiest way to find out would be to do a practical experiment with the spheres that you have.

 

May be you are right, I got a bit lost in this...
I plan to use those little spheres they use in hunting rifles, I dont know exactly which one, but I think they should have a diameter of 1 or 2 mm.
As you say, the best thing is to make a test! We are in lockdown mode in Italy, so I'm not sure when I'll be able to have my hands on them.
Anyway, I want to finish the design all the details of the hull first.

Be sure I'll let you know the correct percentage when done

 

Dear All,

Here is another question I need to find an answer to.
I am in a bit of trouble when deciding about the dimensions of the plywood to use.
I'm using Dave Gerr's book on scantlings, but I'm not sure I'm doing it properly.
I would like to use 16mm plywood for bottom panels, and 14mm for sides. Do you think this is correct?
I guess I should increase the dimensions of the bottom in the area in which the keel will be bolted: would it be enough to increase it to 26mm in that area (I would add a second layer of 10mm ply)?

The design is 7.5 meters LOA (25 feet). I designed 7 bulkheads, and I plan to use a 4mm plywood to build them. Do you think this could be fine?

Thank you in advance you any suggestion you can give me.

DVV

 

Little update: On a deeper look, Gerr's book - and the kind advices of a designer I keep on stalkering with my questions on his social media - gave quite different dimensions.. I need to rethink the scantlings.
I also added a couple of longitudinal stiffeners that were missing, had to move the cabin floor up a bit, but now the mast partner area looks much better.

I need to update the project with new ply dimensions, and adjust the calculation accordingly.
Then make a test with lead spheres to understand the weight of a keel full of them, and epoxy to full it. Adjust the keel weight and position to account for those changes.

I have a copy of Rhino3d for mac. I would use Freeship to develop the curved plates of the hull, but, can I use Rhino for the not curved ones? That would allow me to have a better shape of the bulkheads, because I could use the hull to trim them according to its shape.

DVV

 

What is the reason for the multichine? On a flat bottom boat it would make the boat pound on the waves when sailing upwind heeled over.