W17 Trimaran?

Mike, I read the article in Pro Boat-that was some brilliant thinking on your part-thanks for sharing it with the rest of us!

 

In reply to 'upchurchmr'

Most of your questions will be answered when you read the latest article, so I suggest you order it from PBB if it’s important to you. Otherwise you are just stabbing at conclusions that are often not taken in context.

There are far too many variables to say one shape is always better than another. First of all, there‘s the owners design criteria to consider or, if someone wants to build in composite foam, then a round bilge boat could be dictated simply by that. Also, for lower speeds, round bilge has less resistance, so if the boat is to be used in an area of low winds, just that could be a reason for choosing round bilge.

For your info, my larger W22 was actually designed BEFORE the W17 even though plans were not available until later. As I’ve clearly stated on my website, the W22 was based on the successful Magic Hempel but is about 10% smaller. The W17 in comparison, was initially designed for the flat beaches of the Philippines and to also be trailed on a flat bed … so the flat bottom was a natural initial choice. But in working through the design and now having sailed 1000+ miles and 4 seasons of experience with my own boat, the design has proven to perform even better than I had hoped. And there are significant differences in my ama design compared to those of either the Strike or the Seaclipper that you mention, plus there are other detail differences too numerous to mention here. All these boats have features their designers will defend so you’ll need to consider all the details before casting judgement. But you cannot categorically say ‘a round bilge boat is always better than one with a hard chine’, or vice-versa. You can only consider ALL the differences and see how things add up for any particular craft, together with the operational duties it’s expected to perform. There are always trade-offs .. such as ‘round bilge has the least frictional resistance (that mostly affects low and very high speeds .. but hard chine shapes (IF well done) can show less wave-making resistance in the mid-speed range AND show less leeway’. And these are only just a couple of examples.

So please, try to trust experience. For example …. if you double the buoyancy of an ama, the maximum bending moment on the beam also potentially doubles …. so it’s not ‘a small incremental change’. Beyond this, I can only suggest you do your homework before jumping too quickly to conclusions that may be false. Happy research.

 

I have tried to contact PBB to get a copy. Haven't gotten an answer yet. I'm not going to find one here in northern Texas on a news stand.

Interesting that the initial design was to allow transport on a flatbed. That makes the choice very easy - at least for a start.
I'm certainly aware that the development process might easily show other benefits or ways to minimize the performance impact.
Certainly a flat bottomed slab sided hull will reduce leeway, but is it the most efficient way to get leeway prevention?
Coming from an aerospace background, I seriously doubt it is "best" for performance. I don't doubt it does reduce the requirement for board size. Another issue that does not immediately concern me.

If vertical sides are indeed the way to minimize wave impact/ splashed water, that can certainly still be done with a round bottom. So that does not seem to be a discriminator. Having sailed a Tornado catamaran in my youth, I can say that a (mostly) vertical side does not stop splashing or wave impact in all sea states.

As far a casting judgement, that is the only way any interested sailor can evaluate boats, isn't it?
Making statements and waiting for a response seems to be the only way to get designers to reveal enough to make an informed judgement. Most designers say - " trust me and my experience" and "what you see is what you get".
Sorry, but in my professional life the only way progress was made was to challenge the current design and evaluate the resulting information.
You yourself are saying exactly that in defending the flat bottom design. "Defending" is probably not a characterization encouraging discussion. Perhaps explaining would be a better term.

I really don't understand your discussion about increasing ama size.
Let me assume your ama volume is 80% of the total loaded boat displacement.
If you increase the volume to 160% you don't increase the load on the aka by double, because at something over 100% the boat will be blown over - turtle. The 100% volume and the spacing to the Weight CG provides a natural limit to any developed loads. I'm ignoring impact loads from gusts or waves for the moment.
So in the admittedly simplified scenario, the load increases 25%.
That does ignore the additional weight of the ama increasing righting moment.

Trust me. I do agree that I don't have professional experience designing large ships. And I do recognize your qualifications. But not everyone is clueless as you seem to assume.
Nor do I claim expertise here. I just want to understand. Before I choose a design.

Marc

 

Sorry Marc if you're not liking my explanations. But your blunt reaction to them is just why designers do not commonly enter into debate on a forum .. it's just too time consuming and frustrating. I was not 'defending ' anything ... all ideas have some merit even if they only make you think, and I most certainly did not say that you or anyone else I interact with, 'is clueless'. That's totally of your creation and I am sorry you feel like that. So I will 'bow out' at this point and let you do your research how you choose.

 

Typical, you didn't actually say anything.
I'm still going to read the article and see if there is anything there.

I really don't want debate, I want some facts.

Good to know the design was based on flat beaches and a flat bed trailer - that seems to be a fact.

I'm really frustrated with the lack of direct responses. No comment on increasing load with ama size? Seemed like a pretty easy / non controversial thing to answer. It all comes down to math. Or did I miss something sufficient that my statement was wrong - I don't expect an answer, of course. You already demonstrated that method of conversation. That response said to me you think the question is so "clueless" that it didn't merit an answer.
You never said it, you just demonstrated the attitude.

What puzzles me is that the design is good enough and interesting enough that it is still my #1 candidate.
What can be the problem with actually understanding your design choices? And relative benefits of features - round bilged vs flat bottom for instance.

 

@ upchurchmr
I have appreciated your contributions on this and other sites over several years but in this instance I am in sympathy with "W17 designer".
I am sure it was not your intention but the tone of your posts came across as confrontational.
As this article is in a current publication it would not be appropriate to post it elsewhere.
@ W17 designer interesting concepts, I look forward to reading the article.

 

Please review the conversation and see if there was any actual response to any of my questions.
No doubt my frustration is evident.

In fact, the designer does not have to respond at all. There is no "requirement" for anyone to back up their statements.

What you don't see if my previous private attempts to understand the design's basis. If asking a direct question is confrontational, so be it. I can and have read the vague explanation on the W17 web site.

 

The October-November 2017 issue of Professional Boatbuilder, #168, which has the article by Mike Waters about his W17 trimaran design can be downloaded for $5.95 at the WoodenBoat Store website: PBB 121-Current https://www.woodenboatstore.com/category/pbb_121-current/6

 

Thanks, I hadn't followed up yet.

 

This may seem an odd first post as a new member, but, having come across this in looking at the W17 as a possibility for my "first build" boat, I too think the designer is quite justified in "disconnecting" with someone who is arguing for things that whose fundamentals don't appear to be well understood, and I thought I'd explain why.

Math, and design assumptions, you can't separate them in engineering load structures. The poster clearly considers that the load increase is minor given the constraint that the design weight on the amas doesn't change (much), i.e. +25% weight and +100% amas volume = 25% more load. Its not this simple. The designer does clearly state that its designed to fly a hull only with one aboard, and if one is increasing the buoyancy, you should consider that someone, sometime, is going to push the loading and thereby reach forces developed by the full floatation load the new amas can take. This would imply that good design should have the aka take the load of a submerged amas even if you are only designing for 25% more load windward. This is only one reason that comes to mind - another, more complex to illustrate, is that sailboats don't operate in a static loading condition, the forces are dynamic (i.e. change over time) and the inertial effects of a gust and the time it takes the boat to accelerate over and capsize the boat will (just from the amount of rotation required) exceed the time needed to submerge the float, and in such conditions, dynamic loads could well mean that theres more than a 25% increase in loading compared to a design intended to shed the load by submerging the lee amas. Consider it this way, if you push on a wood slat held in place with a small weight (think steady breeze), you can move it aside, if you punch it hard (think gust), with no more support on the slat than the push, you can break it, even though the "supporting" mass is the same.

Anyhow, old thread, so hopefully I'm not breaching etiquette being new here in replying, but complaining that designers don't share detailed responses while taking an approach that seems to some a little argumentative seems counterproductive, and I at least wanted to illustrate that the designer does have good reason to insist that a doubling of amas volume doesn't just require incremental aka strength improvements. In fact, I'd question his design skill if he HAD agreed to double the float volume without seriously considering the knock-on effects on the rest of the structure.

 

I have some experience with tri's and cats with various hull forms, both hard chine ply and round bottom foam/glass floats. Float beam and volume distribution/prismatic coefficient combined with weight/sail area make ALL the difference. Round to hard chine comparisons are barely worth considering on a recreational boat. Trust your designer!!
I notice that several of the latest fast hulls, both multi and mono are using hard chines toward the stern to help separate the wake at speed.
I do think that higher volume floats, with proper design, are better and easier to sail. However, you can't just make a small float bigger- it will only be drag.
B

 

Wow, only a year late.
OBTW, I was a structural designer for military aircraft.
Not the same, but the engineering principles still works the same.

 

Late is relative, I read the thread today. It got me to finally make an account, so I'm taking that as a good thing

Yes, it does.