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Author Topic: hull design  (Read 2185 times)

lgosdset

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hull design
« on: January 18, 2008, 05:42:16 PM »

evening.

just trying to work out some angles, what is an acceptable angle for a deep vee hull at the aft of the boat?
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glennb2006

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Re: hull design
« Reply #1 on: January 21, 2008, 01:32:41 AM »

Ideally as flat as you can get away with for good speed....
There are many different angles out there on the models currently being run.
Glenn
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ids987

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Re: hull design
« Reply #2 on: January 21, 2008, 01:21:45 PM »

I think (although I can't find a hard and fast definition), that deep vee defines deadrise at the transom of more than about 15 degrees - where deadrise is the angle rising each side above the horizontal. Classic deep vees have a relatively constant deadrise along the straight or relatively straight part of the keel. Between 20 and 24 degrees or more would be relatively normal for a classic deep vee. Higher deadrise angles cut through waves and chop better, and hence tend to "ride" better on rough water. Lower deadrise angles will make for a faster boat, and greater stability on flat water. There are hybrids as well - where the boat is relatively flat at the transom, but the deadrise increases up to the "breaking point" - the sharp curve in the keel. The idea being that, if the boat rides relatively flat, the sharper deadrise towards the bow cuts through the waves, but the flatter rear retains most of the planing ability. These are generalisations, and disregard other significant factors like chine rails, the shape of the keel etc etc.
It sounds like you're planning on building from scratch.......

Ian
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lgosdset

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Re: hull design
« Reply #3 on: January 21, 2008, 07:08:38 PM »

yes i am designing my own hull, for fun, if its any good i might be tempted to race at club level, if not then i guess i can buy a ready made one and use that. i have drawn up two designs so far, one is quite narrow, 42" by 10", i am in the middle of building a cardboard model of that one to see what its going to look like. however i think i perfer the other one with is also 42"long but a bit wider 12". i am using a uniform angle of 26 deg for the one so far. i will build both in cardboard and decide which one i want to build. I am trying to keep it simple whith not too many strange angles and frills. I am not expecting it to be competitive or anything its just to see if i can do it really. I have decided on a surface drive prop, and probably a .46 engine, alough i just want tto buy a cheap engine at first to get used to it and test it.
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ids987

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Re: hull design
« Reply #4 on: January 22, 2008, 12:33:21 PM »

If you're interested, you can find a free plan here: http://new.intlwaters.com/FreePlans/gasmono.htm

That one is for a 48" boat, but should be quite easy to scale down (I think I have seen the same plan scaled down to 26", and scaled up to 72"), raise the sides (freeboard - if you want to make it OMRA compliant), stylise with your own hatch design etc.
I haven't built one of these, but I suspect it may be the same design that one or two from this forum have built - with success. Like here: http://www.modelboatmayhem.co.uk/forum/index.php?topic=2820.0
Even if you don't want to follow someone else's design, it may help to focus some of your ideas.

If you do get "the bug" - and want to race, you will probably need to consider how to transfer your hard work to fibreglass.

Ian
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lgosdset

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Re: hull design
« Reply #5 on: January 22, 2008, 01:03:01 PM »

been looking at that plan and i am really happy because my first plan i drew up looks very similar, apart from a few changes in width and depth.  all the bulkheads and the transom look almost identical. thatks for that link, it has really helped put my plans in perspective and i have changed a couple of thing too. i know freebord is important for omra, but whats the smallest ammout I can get away with? I don't want it to be too deep. also, fiberglass is going to be another issue, I guess i will cross that bridge when i come to it.
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ids987

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Re: hull design
« Reply #6 on: January 22, 2008, 02:40:26 PM »

Hi Chris - just searched through some of your other posts, and found your name.
The term freeboard has just been removed from the OMRA rule book, as it's definition is a little ambiguous. The relevant rule is worded:

12.  All boats (excluding 'specialised designs' such as Tunnel Hulls and Ribs) must have at least 50mm (2 inches) of side height.  "Side height" in this case being the measurement of the maximum distance between the chine rail and deck.

Rule book is here: http://www.omra-uk.org/rule_book.htm

Must say how good it is to see up to date information on the new look website.

Ian

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scoop

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Re: hull design
« Reply #7 on: January 22, 2008, 05:43:15 PM »

Hello chaps, further to the 50mm ruling for ' freeboard ' as discussed, agreed and accepted at the OMRA AGM

Boats designed with rounded or chamfered edges to the deck will have their side depth measured vertically from the Chine Line to a point halfway round the curve or chamfer, measured vertically. Rounded decks are not allowed to meet at the Chine Line directly unless it is a feature of a model of a full size offshore race boat.This proposal was accepted with none against.

ps Dont forget your boat number needs to be a minimum of 50mm as well. I understand the updated rule book will be available soon

Scoop.....aka Stewart Rae - OMRA Public Relations Officer



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w3bby

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Re: hull design
« Reply #8 on: January 22, 2008, 07:37:42 PM »

Purely out of personal interest, does the 2" cover all classes?

The plans referred to above make a nice relatively stable boat, it can get a bit flighty at higher speeds. It is raced successfully by the designer in the US. He has a newer design that hopefully reduces the airborne excursions  :) If you would like a copy of those plans PM me your email address and I will forward them to you.

DickyD

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Re: hull design
« Reply #9 on: January 22, 2008, 08:04:27 PM »

Purely out of personal interest, does the 2" cover all classes?

The plans referred to above make a nice relatively stable boat, it can get a bit flighty at higher speeds. It is raced successfully by the designer in the US. He has a newer design that hopefully reduces the airborne excursions  :) If you would like a copy of those plans PM me your email address and I will forward them to you.
Better send them to Danny Ian, he needs all the help he can get.  {-)
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

scoop

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Re: hull design
« Reply #10 on: January 22, 2008, 11:07:05 PM »

Yes 50mm or as us oldies prefer to call it 2" covers all classes, Scoop
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w3bby

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Re: hull design
« Reply #11 on: January 23, 2008, 12:42:49 AM »

Better send them to Danny Ian, he needs all the help he can get.  {-)
Boat driving as good as his web design then {-) {-) {-) {-) {-) {-) {-) {-) {-)

Sorry about disturbing the design thread.

lgosdset

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Re: hull design
« Reply #12 on: January 23, 2008, 02:00:50 AM »

is this 50mm all the way round the boat? or can you have sections lower than this?
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ids987

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Re: hull design
« Reply #13 on: January 23, 2008, 03:59:07 PM »

50mm is at the point of maximum height between deck and chine rail - so, yes, sections can be lower than this.
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lgosdset

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Re: hull design
« Reply #14 on: January 24, 2008, 02:23:03 AM »

well plans are drawn up, i am quite happy with them, now i just have to draw the component parts full size. I am feeling quite excited. cant wait to buy the engine and running gear!
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martno1fan

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Re: hull design
« Reply #15 on: February 04, 2008, 10:27:47 PM »

been looking at that plan and i am really happy because my first plan i drew up looks very similar, apart from a few changes in width and depth.  all the bulkheads and the transom look almost identical. thatks for that link, it has really helped put my plans in perspective and i have changed a couple of thing too. i know freebord is important for omra, but whats the smallest ammout I can get away with? I don't want it to be too deep. also, fiberglass is going to be another issue, I guess i will cross that bridge when i come to it.

Hey thats my build thread i also changed the boat to my tastes,the sides ar 80 mm at the highest point,omra legal but i dont race so didnt see the need for a cowl.the boat runs well handles rough water too.its not the fastest with the strimmer motor for power but its doing 30 mph on a good day.These hulls really move with a zenoah.Good luck with your build mate  O0.
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