Over built flat deck power cat

Hello,
I am going to build a flat deck cat with a wheelhouse to look along the lines of a wind cat service boat.
8.5 x 3 metres so not massive. I intend to use it in coastal waters and our local Humber river estuary.
The build will be out of marine ply and sheathed in fibreglass. One of many questions I have is can this type build be built too rigid. Obviously weight is always an issue but is flexibility a prerequisite. I've no doubt this will be the first of may questions as this is my first "big" boat build.

Grateful for any advise.

 

Hi @Scopic , welcome to the forum. The single most popular thread on thd forum is @oldmulti 's Multihull Structure Thoughts, which is,as I write this, at the top of the page. Start there. If you're going to spend time and money to build a boat, reading the entire thread is a pretty small investment.

 

No, it cannot be built too rigid. But it can be built too heavy.
Don't confuse the two. Weight is the enemy.

What does a "wind cat service boat" look like?

 

@Scopic are you designing this vessel yourself, perhaps using a larger wind turbine crew transfer vessel (CTV) as a basis?

If so, do you have any sketches that you can post on here of your design?
Or have you purchased a plan for an 8.5 metre power cat?
Please be aware that while you can scale things like hull shape down from a typical 16 - 17 metre (or larger) CTV, you can't really scale down the wheelhouse - it will still need a minimum of 1.8 metres headroom, and it might look a bit large in relation to the rest of the boat.

Here is some background info for reference on wind turbine CTV's -
An Introduction to Crew Transfer Vessels https://www.4coffshore.com/support/an-introduction-to-crew-transfer-vessels-aid2.html

What type of engines do you intend to install on your cat, and what speed are you hoping to achieve?

@BlueBell the attached PDF is a typical example of an 'older' wind cat service boat from 12 years ago, built by Alnmaritec (who are sadly no longer in business )

 

It will take time to go through the entire thread, but @oldmulti has provided a very useful index near the beginning, and you can perhaps look through it to find references to 'small' power cats - he has mentioned these quite a few times in this epic thread.

 

Hi BlueBell,
Wind cats come in so many different shapes and sizes but the inspiration for my design is this.

 

Hi bajansailor,
looks like I've got some seriouss reading to do thanks for the info.

 

Hi,
as you can probably tell I'm useless with a key board and a mouse, however I can knock nails straight and lift heavy things!

 

The type of craft shown in your photos is called a SWATH - I think it would be rather difficult to scale down the SWATH shown to an overall length of 8.5 metres.
@Ad Hoc of this forum is an authority on SWATH vessels, and I am sure that he could offer you some useful advice about them.

But I think that for a 'small' power cat for the Humber estuary you would be better off just going for a more 'conventional' type of hull form - there are many plans available online for 'small' power cats.

Have you drawn any sketches showing what you have in mind?

 

Before you get too far, there is some important terminology. Rigid is a theoretical absolute where a material does not deform regardless of the force applied. To understand engineering formulas and values, the property is stifness (K). For a body, that depends not only on the elasticity modulus of the material (E), but also on the size and shape.

 

Thank you point taken.

 

Richard Woods has a 30' power cat design (Jazz 30) which will suit your needs. Many different deck/cabin arrangements possible.
He has 40-50 years experience as a multihull designer/builder, and is one the most respected in the industry.
Buy the plans and start building.
You will save a huge amount of time, and get a very good boat.

 

I recognise that design

For the length/size of cat you want/need, I wouldn't worry what CTVs or any other boats looks like, in that sense.
You need to focus on what is your SOR (requirements) and go from there.