Complete Beginner's Questions

[James88]

Hi everyone!

First of all, please don't blame me for all the silly questions I'm going to ask. I'm a bit in a difficult situation: I have to design a small motoyacht and I'm practically totally new to boat design and construction. The whole thing is more of a styling project than a real-world conrstruction and engineering project - so I might still have a chance.
The final result will only be detailed 3D visualizations of the design. So I definitly don't have to go into every tiny detail but I still want to make it as tought-out as possible.

The design should convey the racy features of a powerboat with the details of a classical motoryacht. Similar to the Wallypower.
I started by creating a basic hull shape. Since it's a planing boat the hull has a large flat surface at the back. However I'm not sure on the shape of the chine and the jets/propellers.



I've found some books and web sources on boat design but it's quite hard to get the information needed. I'd be happy if you could share your thoughts and criticism as this might be the best way for me to learn!

Thanks in advance.

Best,
James

[drmiller100]

homework question????
what material will the hull be made of?
how big?
open ocean? big lake? small lake?

[James88]

The hull will probably be made of carbon fibre, it will roughly be 15 metres long and should be designed for off shore cruising.

[Olav]

As far as I can judge from the picture, your design won't work properly as a planing hull.

- The chines seem to have a rather large radius, so they won't shed the upcoming water well - especially in the aft part of the hull. Make them as sharp as possible and let them reach right up to the stern.

- A flat bottom aft is good to generate lift, but your afterbody looks like the one of a sailing yacht. Reduce the rocker to zero (i.e. straight keel, immersed transom) to avoid the hull being sucked down at speeds (remember, you want the opposite!), to have more volume aft (centre of bouyancy will move aft as well) and to provide space to put the jet drives in.

- The same is true for the beam: Don't make the boat too narrow aft but keep the lines parallel (or almost parallel). This will increase the lift while under way, provide enough volume for the propulsion plant, give stability and more deck area = more living space for the people aboard.

However, apart from the aforementioned points I like the look of your design, especially the forebody.

[James88]

Thanks Olav! That's very helpful.
I'll try to put that advice into practice and post some updates as soon as possible.

[TeddyDiver]

It looks nice! not a planning hull surely but a semiplanning.. and if intended for somewhat sheltered coastal waters might actually do well..

Originally Posted by TeddyDiver

It looks nice! not a planning hull surely but a semiplanning.. and if intended for somewhat sheltered coastal waters might actually do well..

With some changes mentioned above!

[PAR]

Your best approach is to pattern your underwater areas after well known performance hulls and then "stylize" the topsides as you deem fit. This way you have the assurance of a well founded hull form and the marriage of the contest winning styling above.

[James88]

Thanks for your replies.
Is there any kind of "hull shape library" or something available on the web? Or any books you'd recommend?

[marshmat]

This being winter, there's a convenient hull shape library in the nearest port town- the yachts that are up on cradles for the icy season. One of the more useful exercises in understanding hull designs is to head down to the boatyard and walk around for a while under the yachts. The differences between fast sailboats, slow sailboats, motorsailers, displacement powerboats, semidisplacement powerboats, and (the easiest of all to identify) planing powerboats become very obvious when you see them side by side. If you write down the manufacturers of a few that look interesting, and look them up when you get home, you'll start to get a feel for what hull shapes are used for what purposes.

[TeddyDiver]

My list of recommended books in the order you should digest them..
Dave Gerr, The Nature of Boats
Ted Brewer, Understanding Boat Design
Larsson & Eliasson, Principles of Yacht design
Dave Gerr, The Elements of Boat Strength

[Olav]

Shoot me a PM with your e-mail address and I'll send you some lines plans.

Regarding books: Try to get hold of "Principles of Yacht Design" by Lars Larsson and Rolf E. Eliasson, there's a chapter called "High-Speed Hydrodynamics" in which the most important features of a planing hull are compiled.

[marshmat]

I'll also vouch for the L&E book.... nice reference manual, presents a good overview of a lot of relevant theory, calculations and practical examples.

[James88]

I found that book on amazon.com but I considered it being a book on sailing yachts only. I'll definitly have a look at it!

[marshmat]

The worked example in Larsson/Eliasson is a sailboat, but the hydrodynamic principles and design methods apply equally well to powerboats. The chapter on planing hulls is quite good.