Actual real life boat being built

Nice work!

I am following this thread with interest.

 

Did not want to post that picture because of Kevin's middle finger salute...

 

The angles of each section of hull between the steps are different, and the hull has a 'pad' to run on. Each 'bit' of hull is considered individually, which is the reason for the large step.

In the design for the model, you can see the end result more clearly, as the boat is smaller, and easier to photograph.

It is still the same design concept I discussed with you over three years ago!

 

So when are you coming down for a look then?

ps you can bring the rest of the family if you want - just make sure she doesn't cry!

 

It looks like stepped hulls have come along since the 20s. Do you increase the angle of attack as you go aft? How do you determine the height of each step. It looks to me like a stepped hull could be chosen over a conventional just to control the angle of attack of the hull on plane. Is the reduction of drag still the prime motive of stepped hulls. It would seem to me that if a lot of knowledge and experience wasn't applied fully a stepped hull boat could even have increased wetted surface and increased drag. Is there a concentrated source of knowledge and information or do stepped hull designers keep their "secrets" to themselves and leave everybody else in the dark?

Easy Rider

 

Mostly they leave everyone in the dark...


I worked from the running surface of the boat on the plane - to determine the best running surface and then widened the running surface to deal with the realities of popping in and out of the water. This gave me the profile.

I then worked forward the angle of attack for each section of the hull - which gave me the design.

 

Tricky,
What is the best angle of attack for a planing hull just faster than "over the hump"? With most wings it's about 10 degrees and I'll bet planing hulls are the same.
Easy Rider

 

I dont know if the angle of attack exists as a 'best' - but I found that around 3-4 degrees works best for me. Possibly because the water dencity being different than air? 10 degree would not work in a boat ( I dont think )

Also - some parts of the steps 'carry' more of the boat than others, which also expreiance differnet loads from waves and swell etc, so A single answer is not really possible.

I would guess the easyest way to determine this would be with a non-stepped boat of the same size and weight and at the speed you want, then video the boat at optimum speed, and determine the angle from there.

Remember - a stepped hull does not really 'trim' it resists trim - so the design is really for an optimum speed. My design was optimised for 80knots in English seas.. Either side of this speed I am loosing a little, and on a lake or sea in the USA, I would loose out because of the deepness of the vee and the position of the steps and spray rails.

 

Thanks Trick .. but if you go 80 knots on an Alaskan sea (that you seem to think is like a lake) you will probably experience a voice change to something like a squeak. Bloody hell as I guess you guys say. Thanks for the input though.

Easy Rider

 

My experiance of USA seas is limited to Miami on three seperate visits, and I think we set records on Lake Conniston with more chop. Possibly just lucky? I have never seen the seas around england being anything less than 2 foot chop and usually much worse.

The hull is specifically designed for 4 to 6 foot chop - which is what we usually race in. ( the weather always does something funny a few hours before a race! )

 

Trick,
We get calm seas (not very often) to 8 to 12' seas on inland channels and 3 to over 18' outside. In the summer we get calm seas fairly often and 3 to 5' seas once a week or fairly often depending on the year .. it varies a lot.

Easy Rider

 

I went down to visit the hull.

The hull is such a loverly thing to see in real life. The gaps between the steps are so big you could keelhaul someone and they'd not get wet!

It is definately a very very different design of a three step hull. You can see exactly how it is going to work, and it is very exciting to see it.

 

Good to have you visit and meet the latest addition to the family - see you again soon!

 

If you guys are interested here are a couple of photos to show the Formica covered hull and MDF spray rails

 

Tricky,
It's great to hear designers getting turned on by their work. Is it the shape or the thinking of what it will do on the water that turns you on .. prolly all the above. I remember you saying the steps were at different angles of attack and it looks like they are of less angle of attack in the photo .. I assumed more. If the fwd hull is running at the optimal angle of attack .. why change it? The spray rails look large to me. This hull is so deep it looks like propeller torque could cause unwanted roll/list at speed while on top. Would counter-rotating propellers and the bottom right next to the transom keep things in check?

Easy