Interesting aluminum design

[Stutts]

Type: Round bilge sailing catamaran
Vessel Designer: De Villiers Yacht Design [NZ]
http://www.devilliersyachtdesign.co....loycruisingcat
Size: 19.00 metres
Beam: 9.2 metres
Speed: 18 knots
Launched: 2008
Engines: 2X Yanmar diesel engines
Rating: 75 HP @ 3300RPM
Propulsion: Sail drives
Fuel: 1500 lt
Fresh water: 1300 lt

Designed by a naval architect, this 62' design is for a small scientific team in one hull and a small family in the other. What intrigues me is the forward steering position [just behind the front mast] and the round bilge hull. It must have a massive drainage design for the forward steerage position and I'm not sure how this has been done. Still, a nice looking boat with low windage and obviously built like a brick. I'd love to hear some opinions of this design.

[Ad Hoc]

Every design has an objective...doesn't mean we must all like or agree with it!

So long as the design satisfies the client requirements, what does it matter?

[Stutts]

I wasn't knocking the design or asking if anyone liked or disliked it.

I'm not a designer, so I was just looking to understand the round bilge idea [why round bilge?] and how the concept of the forward steering position might work regards to drainage in serious weather etc. and why might it be forward rather than at the usual rear of the pilot house?

I just put up a humble inquiry, that's all. Wrong forum maybe?

[Ad Hoc]

Stutts

No, not wrong forum. Depends who you ask. If you ask someone who is not a naval architect, they'll wax lyrically about this that and the other...if you ask a wannabe designer, they'll come out with all sort of 'plausible' ideas which sound great when told, but seem odd once you've digested it and if you speak to arm-chair designers, they'll talk just about numbers to you since they have computer programs to do everything for them and don't understand anything beyond an input and an output, if you ask a/the naval architect, they'll tell you about the compromises made to satisfy the requirements from the client and hence nothing is perfect but the "whole" design works and if you ask a hard core sailor, you'll get opines from great to shite etc etc..

No two boats are the same, each has a different "design objective" ie what the customer, the person with the money paying you, wants. If the design "works" for the client, then what ever we think/feel about it is bit of a mute point, since the client likes it.

Does not mean we cannot have our own opinions and comment/criticise it, just means that are opinions are somewhat different to those of the owner! Bottom line, doesn't mean anything...you either like it or you don't.

[nero]

The GunBoat has a forward "hole" and the steering is in the cabin just behind it. I think this idea of forward steering station is to get a more sporty and clearer view.

Round bildges for better performance. ... Or that was the theory a few years ago.

[Milan]

Round bilge have lowest wetted surface area. (especially important for slow speed in the light wind). Forward steering position on catamarans provides better visibility unobstructed by the high cabin and you feel the wind much better. Also, mast and all sail controls are by the hand.

[john schroeder]

I think this is a great design inside steering in foul weather out on good days. Al the lines are worked at the mast base. I think this boat is being built in New zealand. the forward cockpit concept will become more comon I think as the behind the cabin lookout system makes all line handeling very complicated

[Stutts]

Thanks for the replies. The line handling makes a lot of sense [I didn't think of that] from a forward steering position and would be great for mooring, fine weather sailing and no walking around the side decks to go forward.

Thanks for the heads-up regarding round bilges. Probably carries weight better too.
Nice to see a cat design that hasn't got those wrap around plastic windows. It's a wonder why more cats from 40' up aren't made with aluminum. All production cats seem to be glass only. Due to cost I guess.

[brian eiland]

Hello Stutts,
I noticed you were from Australia.

Where did you get the photos of this vessel,..in Australia or New Zealand?? Do you have any more?

[Stutts]

Yes, a NZ designer. the site of the designer:
http://www.devilliersyachtdesign.co.nz/

Click on STOCK designs > under 'sail' click on '62' Alloy cruising cat'. There a description of the design and plenty of photos of the construction.

Completed in 2008 and Built by Q-West boat builders Wanganui NZ:
http://q-west.com/19metre-sailing-cat-detail-sheet

[Milan]

Originally Posted by Stutts

… It's a wonder why more cats from 40' up aren't made with aluminum. …

Fatigue, weight and unsinkability are major issues for multihulls …

There were some interesting discussions on the forum about these things before. Here is the one of the threads:

Material strength and fatigue

[Ad Hoc]

Milan

Fatigue is only an issue, regardless of vessel size and material selection, if the design has not accounted for it and its deleterious effects.

[Milan]

Originally Posted by Ad Hoc

Milan

Fatigue is only an issue, regardless of vessel size and material selection, if the design has not accounted for it and its deleterious effects.

Well, it can be done, but, nature of aluminium is such that it is rather difficult to combine light weight-unsinkability- good fatigue resistance in a simple, fast and inexpensive building process - compared against alternatives, for example strip plank epoxy glass sandwich of any other foam or wood sandwich techniques.

The lightest aluminium hulls, (still considerably heavier then sandwich), would have plate thickness of 3 mm and a lots of stringers, a lot of welding and would need complete insulation.

In the seventies and eighties number of aluminium multihulls were built. Most of them had a lot of structural problems.

I think that aluminium begins to make sense for cruising multihulls around 20 m LOA and above, not shorter then that.

[Ad Hoc]

Milan

That is where you and I differ

1) IF you're references for "poor designs" are from the 1970s and 80s, then i'm not surprised, there were plenty of them around at that time.

Aluminium today is totally different, well certainly when done correctly in terms of its design and its manufacturing (since approx 90% of fatigue failures are attributed to poor manufacturing, not design), produces a very suitable structure. In terms of weight and longevity.

2) A standard "light weight" GRP sandwich or otherwise layup, is approximately the same weight as an aluminium structure. It is a myth that you 'save weight'.

Ive designed so many structures in both, where the client "thinks" they are making a saving, when the reality is not. Bog-standard GRP hulls weigh the same as ally one, given the same rating, service, design conditions. Exotic composites however, that is a different matter.

So.."it can be done"..yes and is done far more frequently than you imagine. As I stated above, regardless of its size, material choice etc, so long as the effects of fatigue in the design and manufacturing have been accounted for, you'll have a very satisfactory structure/design that'll last for many years.

[Stutts]

What the designer says about this boat and it's weight:

'To keep the weight down we are using Sealium alloy which is 15 to 20% stronger than the conventionally utilized 5083 grade. Recent price increases for petroleum-based products (resins and composites) will mean that building a one-off structure such as this in alloy will be cost effective and not break the bank. In terms of her cruising objectives the boat will be tough and safe and yet not overly heavy, just what the client’s are after'.

And as to staying afloat, plenty of watertight bulkheads?:

'In terms of damaged stability this boat is just about as good as it gets. We have a watertight collision bulkhead up forward and then the forepeaks are separated from the rest of the accommodation by a watertight bulkhead. Similarly the aft enginerooms are separated from the accommodation spaces making 3 watertight bulkheads in each hull'.