Sliding in turns -PLANING HULLS

[eightwgt]

I have a questrion for the experianced designers here. What are your thoughts about reducing a planing hulls sliding thru a turn. I am reffering to small hulls 14-18' with an almost flat bottom.

What can be done to minimize this ?

Rounding the chine ?
Strakes ?
'Reverse strakes' at the chine ?


????

Thanks - I look forward to input.

[FranklinRatliff]

I have a questrion for the experianced designers here. What are your thoughts about reducing a planing hulls sliding thru a turn. I am reffering to small hulls 14-18' with an almost flat bottom.

What can be done to minimize this ?

Rounding the chine ?
Strakes ?
'Reverse strakes' at the chine ?


????

Thanks - I look forward to input.

It's called a skid fin. Unlimited hydroplanes have been using them for decades.

[eightwgt]

I should have addressed that - "No skid fins"

I am reffering to a typical recreation boat-think fiberglass Jon boat - not a performance hull such as a hydro...

Thanks - I appreciate the input - :)

[FranklinRatliff]

If you're going fast enough to be sliding in a turn, you're going fast enough to be thinking about a skid fin.

[eightwgt]

Franklin

Thanks - I agree, however I am looking for other ideas

[kach22i]

You might get a little insight if you read this whole thread.

http://boatdesign.net/forums/showthread.php?t=11121
jehardiman; At most planing boat speeds, side velocity due to a turn is negligable compared to ahead velocity. While a jet boat can achieve significant side velocity in a turn , it is unlikely that a propeller driven craft can. But Yes, if you somehow managed to break a conventional powerboat into a sideslip without flipping it, then the prop will provide significantly less thrust due to inflow AOA effects. I mentioned it because it is a common proplem in auzimuthing pods. Turn the pod at right angles while going fast and you don't get the response you expect

[tom28571]

To stop sliding in a turn, you must have some lateral resistance. Messing with the chines is not the best way. Strakes near the centerline of the bottom like a keel will do the job. One strip on center will be most efficient but two off center is easier on dragging the boat around on the beach. You need to make trials to determine how deep they/it need to be. Stop the strakes well short of the transom (14" or more) or the prop will ventilate on turns. Strakes on the chine can flip you over on a flat bottom boat. The easiest solution is a skid fin but they can get in the way.

The long keel or strakes may also help in making the boat bank inward in a turn.

The worse thing is to have the boat slip in the first part of the turn and then suddenly grab hold. Better have on a good life jacket. Done that on a speedy flats boat and cracked ribs are no fun.

[eightwgt]

Tom

Interesting reply.....

A flats boat huh ? Which one if ya dont minf me asking ? You can send a private reply if you prefer also...

The hull Im working on I know will have sideslip due to the nature of the hullform.... I was simply looking into ideas to safely limit it if possible.

[buckknekkid]

To stop sliding in a turn, you must have some lateral resistance. Messing with the chines is not the best way. Strakes near the centerline of the bottom like a keel will do the job. One strip on center will be most efficient but two off center is easier on dragging the boat around on the beach. You need to make trials to determine how deep they/it need to be. Stop the strakes well short of the transom (14" or more) or the prop will ventilate on turns. Strakes on the chine can flip you over on a flat bottom boat. The easiest solution is a skid fin but they can get in the way.

The long keel or strakes may also help in making the boat bank inward in a turn.

The worse thing is to have the boat slip in the first part of the turn and then suddenly grab hold. Better have on a good life jacket. Done that on a speedy flats boat and cracked ribs are no fun.



bin there done that many times. I throttle so its my fault.

[tom28571]

This particular boat was designed and beautifully built by John Martin of Charleston, SC. He was experimenting with skegs to control the unnerving skids and had installed two parallel ones off center. We were running pretty fast, how fast I don't know but d***m fast and showing off a bit after a big fast boat tried to outrun him. He went into a full bore turn and everything was OK for a while although the boat was skidding quite a bit when it suddenly dug in and I catapulted across the boat. Non tripping chines would have helped too and the lack of them may have been the major fault in this situation.

Maybe I was only bruised rather than busted but a strong lesson anyway.

"Good judgement comes from experience.
Experience comes from bad judgement."

[eightwgt]

Tom

What do you define as a "non-tripping" chine ? I am not sure I understand what type of chine you are reffering.

Thanks again

[tom28571]

Looking at the boat from aft, the bottom will have a portion of the width turned up near the edge. This keeps the chine from digging in when the stern slides sideways in a turn. Don't forget that the stern of boats with the propeller in the stern always slide sideways in a turn.

[eightwgt]

Tom

How much of a turn up ? Do you have an example I can look at ? This sounds like a good idea to incorporate into my project.

Thanks once again - it is appreciated

Tom

[tom28571]

I don't know of a fixed number but you can look at the link below. The view of the stern gives an idea of how it was done on this boat.

http://www.woodwindyachts.com/Restorations/TorpedoRest.htm

[eightwgt]

Interesting..... Thanks.

Take a look at my example.... A-B-C-D "A" being 'standard'....


http://216.84.198.232/chines.jpg

[SamSam]

Look at Carolina Skiffs. The more HP the boat is rated for the more they deal with side slip. Also look at different jon boats. B and C will help prevent grabbing but not side slip, in fact they may promote it. Sam

[eightwgt]

I have seen Carolina Skiffs MANY times =) I have seen many small skiffs. I in fact build boats. I came on here and asked to question hopoing to get some other professional opinions on the re3ar end of a skiff as I am designing a new boat (16') for our line of boats. Considering some of the people known to frequent some of these forums thought Id see what I could hear.... anyway - I have seen about any skiff you could mention although I have not been on all of them =).

I am leaning towards 'D' or a variation of it and C

Thanks guys.....

[Ike]

I am all too familiar with the Carolina Skiff and it's problems. In it's earlier years there were many problems with skidding and chine tripping. Then they modified the chine slightly and added two strakes on the bottom. They will still do funny things if you push them too hard but that can happen with any flat bottom boat. They don't have the kinds of problems they had when they first came on the market.

You would be wise to avoid a "hard" chine for two reasons. One is the skidding and tripping problem. The other is that the Coast Guard has seperate formulas for calculating horsepower on a flat bottom hard chined boat, and other boats. You can put more horsepower on a boat that doesn't have a hard chine. They consider any curvature or angle to the chine, to not be a hard chine. C or D would be a good way to go. I would still put some small strakes on the bottom to give it some straight line directional stability. In other words, make it run in a straight line when on a plane, rather than skitter around or crab at a slight angle.

[Pipex]

That pesky bunch of water enthusiasts have been using this for years. See Quick Release Rails by Hawaiian Island Creations. It was a "gimmick" then and is a "gimmick" now. There is no way of making a flat hull go round corners fast without sliding. Designers wont tell you this but even V hulls slide, thats the nature of water. There are only way of limiting the slide.

[FranklinRatliff]

That pesky bunch of water enthusiasts have been using this for years. See Quick Release Rails by Hawaiian Island Creations. It was a "gimmick" then and is a "gimmick" now. There is no way of making a flat hull go round corners fast without sliding. Designers wont tell you this but even V hulls slide, thats the nature of water. There are only way of limiting the slide.

Maybe then I was right to suggest a skid fin if someone absolute positively wants to limit sliding.

[Pipex]

Yes you are entirely correct. However, I do appreciate that I am probably one of the younger generation of marine engineers. Although I have tradition in the fact I learned with my hands. Still where I am from theres thrusters, bonzers, twinnies and single fins. "Skid fin" seems an outdated term for the modern generation... A generation where we pride ourselves in our skill at slide slipping corners quickly!

As we often see with trim tabs, see recent design issues facing the Viper jet boat trim it is difficult to achieve a firm palcement of a trim tab under such loading. Henceforth considered as the major problem associated with fitting a fin or fins to the bottom of a boat.

Personally I like the Willis brothers idea of golf ball shaped indentations on the hull which create air pockets for which the hull to slide coupled with a deep single to double concave.

This invention leads to another interesting development commonly known as the cathedral hull, and similarly "winged" powerboat which are all further developments of this idea.

[redfury]

quite an interesting read here. Of course, it throws my curiousity into a twist... I'm curious as to what level of effect of "sliding" I'll feel with my Glastron Tri hull since the "tunnel" goes straight to the back of the boat...

From what I'm reading here, it seems that this design would be superior for handling vs. a standard "v" hull configuration.

Which begs the question then...why did they stop making "Tri" hulls?

[tom28571]

quite an interesting read here. Of course, it throws my curiousity into a twist... I'm curious as to what level of effect of "sliding" I'll feel with my Glastron Tri hull since the "tunnel" goes straight to the back of the boat...

From what I'm reading here, it seems that this design would be superior for handling vs. a standard "v" hull configuration.

Which begs the question then...why did they stop making "Tri" hulls?


Some degree of sliding at the stern is necessary or the boat would never turn at all. You could say the front end of your car "slides" in the same way.

Multihulls generally slide less than monos and are more difficult to turn or maneuver because of it. The tri hull is in many forms but falls in between the true multi and mono in these respects. The craze for the deep V may have been a major factor in reducing the number of tri hulls being built. It's the marketplace factor. A deep V on a lake where chop and waves are limited is way overkill and very inefficient to boot. The tri is more stable than most monos and is also rougher riding in chop than a moderate to deep V.

You don't need math to reach these conclusions. Just imagine what is happening when the boat is in motion.

You rarely get one desirable attribute without giving up something else.

[Ike]

WHy no tri's or what was also know as the cathedral hull. 2 things. Fashion and harsh ride. You still see a lot of them around though.

[redfury]

Well, I'm happy with the "fashion" of my trihull, but then again, there are some really ugly trihulls out there. The ones that have the block front ends are the worst looking things out there.

I'm quite happy with the design of my 74 Glastron V178 ( though I'm finding that it isn't the most well built boat out there for its age )

[eightwgt]

Hey guys.....

I wasnt talking about tri-hulls !

Just a simple concept as my drawing shows.....

Im not trying to stop it from sliding, just looking for ideas to make slight improvements - I have to keep the aft end flat for shallow draft....:D

[redfury]

Sorry, didn't mean to change the subject!

Contribution!

What about using those planer boards on the back of some boats? Have the one on the inboard side of the turn dip down harder, like a surfboarder putting his hand out and dragging the water during a tight turn?

[eightwgt]

No problem... it is easy to get off the subject and start discussions.... I know ! :)

All I was looking for were ideas regarding the hulls chines near the transom - no attachments, tri hulls, etc...

[messabout]

Take Tom's advice. Attach a pair of skids to the bottom of the boat. Even a pair of small ones will make a remarkable difference. Three quarters to one inch thick and perhaps an inch and a half wide. Put these on at about the quarter beam locations. That is to say about half way out from the centerline. Do not put them at or too near the chine. If you do the chance of tripping will increase. These runners can be simple wood strips bedded in compound, not epoxy, so that they can be easily replaced. The runners may actually make you boat a little faster. If you have way too much power on the boat you will just have to reduce throttle when turning unless you are into stunt work. Skidding is bad news, but flipping can be disasterous because you could end up with the boat on top of you. Been there, done that.

The non trip chine is a standard feature of fast boats. They dont need to be very big, but bigger is usually better to prevent flipping. On the other hand if they are too big they will contribute to the skidding tendency. That feature will be difficult to install on an existing hull. Try the runners first.

[wdnboatbuilder]

how about the simplist solution................. 3/4x3/4 keel rounded with a fillet. it will make your boat stick in a corner. also end the keel about 30" from transom.