Polaris have a good reputation for there boats as well as four othere contenders In the Vancouver area of Canada.
Northwind USA also have a good reputation as far as Seattle is concerned for ribs.
There are lots of Alli boat builders around that area,therefore the competion is competitive.
Why do you want an Alli Hull ?
A prodution GRP rib will be cheaper and easier for you to get.
Polaris can supply both Alli or a grp hull I am sure,If you are making a serious enquiry and rely want an alli rib I will pass on a telephone number to you of an alli Canadian builder based in Vancouver who builds alli ribs and he can talk you through your requirments.
I would also recomend you speak to Polaris ?
As far as tubes go then I use UK tubes 1850 decitex built to Solas spec and will be sending them out for fitting,as I know the spec and quality.
As far as stability on the water goes Ribs in the main are just brill,If your wanting stability data for your own proposed craft,then talk to the builders as they will have the info and need to clearly define your intended use ?
If you Pm me I will send you a telephone number of somebody who you can talk to who will advise you and builds Alli ribs and also uses them out there.