Trimaran with Parallel Rig

Discussion in 'Multihulls' started by lane, Mar 12, 2023.

1. Joined: Dec 2005
Posts: 38
Likes: 2, Points: 8, Legacy Rep: 10
Location: Austin TX

laneJunior Member

Does a trimaran with a parallel rig with 50% of total sail area on each ama, require a larger ama than a trimaran with 100% of the sail area mounted only on the vaca?
Thomas in Texas

2. Joined: May 2019
Posts: 2,193
Likes: 1,333, Points: 113
Location: australia

oldmultiSenior Member

Lane (Thomas). Can we start with a few basics. If this tri is the 8 foot experiment do as you please as you will learn a lot without much expense. Floats for 8 foot boats can be from "training wheels" to full size sailing floats. But I will talk about basic principles from here.

A tri is a stabilized monohull. The float volume (displacement) can be from 80% to 200% of the displacement of the total boat. It does not matter if there is a mast on a float as long as the float has enough volume to keep the mast base out of the water. Also the float structure has to be strong enough to handle the mast loads. If the mast on the float is next to or on the crossbeam to float connection it should be OK. If the mast is placed between the 2 cross beam to float connections the deck will need to be reinforced to handle the mast loads.

The problem of biplane rigs (mast on each float) is that the wind on the sails unbalances the boat on different angles to the wind. IE the windward sail gets more breeze and try's to push the bow in one direction where as with the wind in another direction the "other" sail may try and push the bow in the opposite direction. This is the reason most boats have a single mast centrally mounted.

As i said do as you want, you will learn a lot but also there are many biplane trimarans of 10 to 20 foot out there that have learnt a lot from there experiments. Some people have written there stories up on the web, search them out. PS biplane rigs work better the larger the multihull is because the hulls are thin, they have good centreboards and they can control each sail independently to fine tune the sail pressure from each sail. There are 70 foot long cats that run biplane rigs and are very good cruisers. An example of a biplane rig tri is at:
Very Unique Small Trimaran Approach – Part 3 | Small Trimarans http://smalltrimarans.com/blog/unique-small-trimaran-under-development-part-3/

Attached Files:

File size:
89.4 KB
Views:
38
• Biplane 2.jpg
File size:
104.2 KB
Views:
38
bajansailor likes this.
3. Joined: May 2019
Posts: 2,193
Likes: 1,333, Points: 113
Location: australia

oldmultiSenior Member

Thomas. Bit of fun, if you really want to go radical here is a 40 foot tri that had 3 masts.

Attached Files:

• trimama 1.jpg
File size:
367.6 KB
Views:
39

4. Joined: Dec 2005
Posts: 38
Likes: 2, Points: 8, Legacy Rep: 10
Location: Austin TX

laneJunior Member

Oldmulti,
Thank you for your input, I read the article again, and with your insight, was able to gleen important information that I had previously missed. I know that there will be some interference sail to sail at different angles to the wind. My masts will be mounted in fiberglass tubes the full depth of the hulls, solidly mounted in the hull. I hope to eventually build a center hull along the designs of the Duo/Tryst. I am going to a funeral and will return later in the week.
Thomas in Texas

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.