Deadrises fully explained

[Happy1]

Any takers? e.g the degrees, what they mean. Apparently there is one on my boat, but I don't know where to find it and what it is for.

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[BarryH]

Look at the transom. Take the angle froom the keel to the chine from an imaginarry line coming horizontal from the keel! Got that good. Right flatter the hull is at this point= shallow vee hull less hp to plane, more acute angle= deeper vee hull more hp top plane. Most yanky boats are less than 20 degree deadrise so are shallower vee and more prone to slaming in a seaway. Deeper vee hull as in my tremlett less slamming and more comfy ride.

But in dont end there as you got the shape of the bow sections to take into account and sprayrails, reverse chines and all the rest!

 

[paulineb]

Deadrise is a little more complicated, but basically it is the angle that the 'V' bottom of your boat makes with the horizontal. On a boat designed for the sea, deadrise is important if you want to preserve your spine. The nearer the boat is to flat bottomed, then the more it will slam. The greater the deadrise, the more gently she will hit the sea again after taking off from a wave. However, the deeper the 'V', that is the greater the angle of the deadrise, then the more power the boat will need to get up onto the plane.

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[Happy1]

So, if I have 19 is that a bit OK, I know it is less than 20, I worked that out /forums/images/icons/wink.gif but wandered if that would be OK for general pottering about and going to IOW for the Grand Forum Frenzy.

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[Happy1]

So, the bigger it is, the more thrust that is required, is that right?

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[paulineb]

Yes but as you have quite a small one, I wouldn't let that worry you /forums/images/icons/wink.gif

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[Happy1]

Obviously you are speaking from experience and I appreciate your view on the smaller ones, however I would like to know about the biggest you have had, and whether it affected the ride e.g. at what size does it stop slamming down. Could you please tell me the size you have at the moment, and whether you are happy with it, or if you would consider changing for a larger one. Not knowing much about them, it seems that if you are unhappy with it you can't just change it, you have to get rid of it and get a new one. So it is important that I know my wife is going to be satisfied with the ride, becuase if there is a lot of slamming going on, it is no good far anyone. You see when we go slow we will be OK but when we use full throttle we may then start slamming and the ride would be unbearable. I am so glad I am checking these things out, I wouldn't want my wife to decide shortly after getting it that she wanted one with a bigger one. Why do the dealers not explain all this to you?

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[martynwhiteley]

Ah, but what you really need is one of variable size.

It increases in size when the ride gets more exciting, to reduce the slam, and decreases when all that up and downy bit is behind you, to allow you to glide on in comfort and little effort.

Anyone know the patent office website?

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[Happy1]

Are these extentions? if so how do they fit ? will they fit all types? If my wife fancies an increase in size after we have had it for a while, will this be possible or will she have no option but to change the lot. It is a Glastron GS209 2003 model.

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[paulineb]

Is it warm in here, or is it me?

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[martynwhiteley]

The design is almost complete, one size fits all.

It will be called the "Vee-Agra", made under licence in India.

(Agra = Adaptable Gradient Running Angle)




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[oldsaltoz]

G'day Happy1,

Most craft have a vert steep 'V' at the bow and this tapers to the transom, the angle at any point is referred to as deadrise.

It's worth noting that the rate of change plays a very important part in how well the boat will handle heavy going at high speed.

If you have 20 degrees at the transom and only 25 degrees 2 thirds from the transom, it will plane easy but slam in heavy seas at high speed.

If, on the other hand the point about 2 thirds forward of the transom is around 35 degrees it will require more power to get onto the plane but slam less.

All you need to do is 'slow down' if the hull starts to slam, and be content knowing that you are using less fuel than the bloke with a deeper 'V' who is going faster in the same sea conditions.

The figures quoted above are arbitrary and are intended to provide a guide only.

I hope this helps

Andavagoodweekend Old Salt Oz /forums/images/icons/cool.gif

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[paulineb]

Tommy doesn't slam. She has these things at the front which give a cushioning affect.

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[Happy1]

Thanks /forums/images/icons/smile.gif

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[Happy1]

There must be some posts missing on my new username, I am totally confused!! Am I on the right planet?

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[tr7v8]

Umm, a far from simple subject, as what you are talking about is warped vee as distinct from monohedron. Monohedron is continuous deadrise of the same angle warped vee is where the section changes all the way from bow to stern.
The standard perception of deep vee needing more power to plane is distorted by spray rails and deflected chines.
Most hulls are reasonably deep vee with flatter after sections this provides not only lift to get the boat on the plane quickly but more bouyancy to support then engine weight. Some boats take this flatter aft section to literally be a flat "shoe".
Deep vee hulls have other issues if monohedron as they can have problems with "chine walking" unless very carefully designed.
A bloody complex subject, best reading is " Dhows to Deltas" by Sonny Levi, who designed the Cigarette and others, also anything by Ray Hunt. Both are the fathers of present day hull design.

Glad you asked Peter!

Jim
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[kimhollamby]

Deadrise not the answer to everything

You have to be a bit careful over all of this.

Deadrise gives one clue but it is not everything. For starters, on any boat except for very high performance it varies over the length of the hull, with sharper sections forward to cut through waves and flatter sections aft to provide lift. If you look at the deadrise of many very seaworthy boats at the transom they are nothing to write home about but then their back ends are not supposed to leave the water.

Deadrise tends to be expressed in three brackets:

shallow vee
medium vee
deep vee

The benchmarks move around all over the place but you could say that these are categorised as follows:

shallow vee less than 10 degrees deadrise
medium vee 10-22 degrees deadrise
deep vee greater than 22 degrees deadrise

In reality many so-called deep vee designs are modified vee shapes (or 'warped bottoms' or 'variable deadrise' hulls depending on complexity of shape and/or designer's understanding of them) where the section amidships is close to deep vee territory but aft it is a lot shallower; this is not a bad thing.

It's pretty obvious that a genuine deep vee will cut through the waves more easily and offer a more comfortable ride, theoretically, but it will require more power and in some cases it can be more difficult to drive. It is also more 'tippy' when not moving at speed, especially in small sizes, and more prone to leaning into cross winds.

Secondly other hull components such as sprayrails (the rails that run along the lower hull surface to deflect water and reduce wetted area ie drag), chine flats (flat sections at the corner where the topsides meet the hull's riding surfaces), keel sections (theoretically not an issue on sportsboats apart from the fact that some have the vee sawn off aft to stop prop cavitation, thus effectively making a keel flat), hull steps (complicated but the name gives a clue as to how these work - think flying boat hull where the riding surface rises in notches to encourage water to break away) and even things like large spray deflectors and low rubbing strakes all add to the mix.

Next you cannot beat hull length for comfort - weight is no bad thing either. This is especially so in waters like the Solent where the chop can be especially short - uncomfortable close to the length of your 20ft Glastron in wind against tide.

After that you have to factor in wave direction. Some deep vee hulls are just plain uncomfortable going upwind if pushed hard because they have big chine flats that keep spray well away and give bags of lift but land with a thump -- however they work really well downwind. Some semi-displacement designs (okay a bit off piste for a sportsboater but I'm in full flow) are very comfortable albeit wet pucnhing into the wind but can be a handful downwind. Some sportsboats can also be a handful downwind if there's not a lot of buoyancy forward - ironically often exactly what you get with a very deep vee.

Lastly, crew comfort in particular is in the hands of the helmsman, whatever the hull design. There are important exceptions to the rule but shaking the fillings out of your crews' molars by bending the throttles to the stops in order to minimise the time spent watching their faces go interesting hues of green is not necessarily great strategy.

There's a lot of rubbish written about hull design which is largely based around too many generalisms. Deadrise, if known at amidships and astern, is an indicator but it is no passport to knowing what the boat will feel like.

 

[wakeup]

<A target="_blank" HREF=http://www.patent.gov.uk>http://www.patent.gov.uk</A>

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[byron]

<font color=blue>Don't wanna take issue with you but Sonny Levi didn't design the Cigarette boats. Can't remember his name right now (the dude that did) I believe he was killed by the Mafia or Columbians because he refused to make them drug running boats.

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[Happy1]

Well, Well, that's me occupied for the next couple of evenings !!! It is fascinating to know what is going on to make the boat operate, BUT I WON'T ask how a 737 flies, we would be here forever /forums/images/icons/wink.gif

Thanks very, very much, the fountain has spurted forth it's tremenodous fountain of knowledge again /forums/images/icons/laugh.gif

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