Amateur trimaran design critique

[gonzo]

PVC works well. You don't really need to bond it. A strap of fiberglass over it will hold it in place. Making holes where necessary to run wires is common practice. Remember to drill drain holes along the pipe.

 

[MrMillard]

Hello any and all multihull enthusiasts!

I'm back with another update. Not many replies to respond to this time, so I will just say thank you to those who have taken their time and written something and get on to the information:

Small changes:

1. The overall shape hasn't changed much since the last iteration. I may tweak the ama support towers and the bow shape to make them more slender in the future though.
2. The amas have been made wider again (60cm/2 feet) to increase volume significantly and their L/B ratio is now ~16:1
3. The displacement has been increased slightly (AGAIN!) and 100% main hull displacement and 10% ama displacement is now ~3800kg/8400lbs/134cu.ft. If that isn't enough to support a cruising load I'm at my wit's end...
4. The cockpit has been widened a bit by flaring it out toward the transom to give more room for crew comfort and tiller steering angles. this should also give better access to the cockpit lockers under the seats.
5. I have modeled two supporting rods for the trampolines between the akas, since the trampoline will be too high to have support directly from the amas. These may need supports of their own, not sure yet.
6. The hull is a bit more rounded and smoother.

The big changes!:

1. I have altered the internal layout and fleshed it out considerably and modeled most of the structural elements.
2. The quarterberth/pilot berth beneath the front berth has been moved to starboard and almost all the way aft. It is now partially under the cockpit coamings.
3. The front and aft cabins now have their own "foyer" (the aft one is shared with the quarterberth) and more resemble cabins from a typical monohull. These have room to stand and get changed etc. The front one could even be equipped with a small sink to enable freshening up or brushing teeth. The front one also has an extensive wardrobe.
4. The head is directly connected to the shower and the potential washing machine shelf is in the head compartment.
5. The galley sink has been moved to the port bench, but is still fairly central. The end of the galley bench (right by the companionway) doubles as a nav area and has room for instruments above, next to the kitchen cabinet.
6. The space for appliances now consists of: 2 x 55cm/~1'9" shallow bays and 3 x 60cm/1'10" full size bays. The two smaller ones are under the starboard settee seats. One of the larger ones is at the forward end of the galley to port. The two last ones are to starboard behind the settee. One is made to be accessed through the head and one from the settee. All 5 can have their appliances be lowered into the boat through the large roof hatch above the table and installed from that access point.
7. The bow has a deep chain locker where the chain goes through a tube down to the bilge and a shallow locker for sails or fenders etc.
8. I have modeled some possible shelf layouts and panels, but not all cupboards and doors to them (for example the cupboard above the galley bench or the area beneath the settee foot well).

I don't know what else I should point out. If you have questions or want additional photos, please say so. I'm mostly interested in your opinions regarding whether I'm headed in the right direction or not and what needs improvement. Or, if you think it is starting to look reasonable, what my next steps should be.

I also have a new question (the entry into a wet area is scrapped for now);
If you were to install inboard propulsion, would redesigning the aft to resemble a tunnel or upside-down U to shroud the propeller be a bad idea? To provide protection from side (and potentially bottom) impacts?

Cheers and enjoy the new screenshots/renders!

 

[gonzo]

A point that has not been brought up. What are the regulations for a boat built and designed by an amateur?

 

[rberrey]

gonzo, I would think that would depend on where it was designed and built. That aside if I were going to put that much money into building a boat I would at least pay a NA to look at the lines, supply scantlings, and back check my work. I think the design is starting to look good as far as design criteria, and be more reasonable in expectation -v- size boat, sailing ability may be another matter .

 

[gonzo]

It is being designed and built in Sweden

 

[MrMillard]

Hello again!

@gonzo, as far as I can tell, there are no requirements for boats of this size if they are built as a one-off for private use and are owned and used by the original builder for at least 5 years after first use. Otherwise you would have to CE-certify it (EU-standard). There are a lot of rules regarding that, but also plenty of guides. If this project ever takes off, I very much doubt there would be any commercial aspect to it, so I would only be answerable to myself. As pointed out earlier in the thread and just above by @rberrey though, the prudent thing would be to get some professional help (or professional skills?).

@rberrey, I have stated before that sailing ability is not highest priority in this cruising concept, but out of curiosity, what would you change to improve that aspect?

Finally, I have another question. Let's say that I wanted it to be fairly well insulated (northern climate and all); would it make more sense to increase the thickness of the structural foam in the sandwich lay-up to gain additional stiffness, or build to specifications and add insulation separately afterwards? Installing insulation separately would require an additional layer as "lining" and would make the insides of the hull quite soft, right? But it might still save enough weight to be worth it that way (no structural loads to support so insulation foam could be less dense?). I'm curious if there is a universal answer to this or not.

Cheers!

 

[MrMillard]

I forgot; I checked the 3d software once more for some updated numbers.

Vaka displacement at 50cm waterline = 3102l/kg / 6839lbs / ~110cu.ft.

Ama displacement (each) at 50cm waterline = 393l/kg / 866lbs / ~14cu.ft.
Ama total displacement (each) = 4557l/kg / 10046lbs /~161cu.ft.
Ama displacement as % of total = 117%

Total displacement at 50cm waterline = 3888l/kg / 8572lbs / ~137cu.ft.

Cheers!

 

[rberrey]

MrMillard , all of my experience is with motor boats and not sailboats . I have had many bad days working from a boat due to waves and strong current , but my worst days have been when you add wind to the other two . I may be wrong but with all the head room you have in your design I am assuming wind will be a big factor in sailing ability . If you have never had to drop your anchor , or keep your bow into the waves in a strong squall , you may not appreciate less head room over more .

 

[Bobuk25]

A place for wet gear is great. I lived aboard for a number of years and struggled with no place to stick stuff. Now I have a wheel house type structure in Stainless that gives me a big space up front to just throw stuff and even though it is not a wet locker as such, it just makes life so much easier.