# Reverse Chines?



## MariettaMike (Jun 14, 2012)

I'm seeing varied applications of reverse chines on some newer boats and and am left wondering what the pros and cons are? And how fast do you have to go to really get any lift benefit?

these seem kinda extreme and might be tough to spin the boat with a pole while dragging on mud bottom


these appeared to be similar in the plug...


...but the finished product is staggered at the stern.


these look like they're in the right place to give lift at higher speeds going straight or turning


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## Backwater (Dec 14, 2014)

It's not so much the "lift" as it is knocking the water and spray back down when running. Lift strakes provide lift. Those pics of hull bellies you have there have no lift strakes. So the pros of outside chines? They knock the spay back down to the water, thereby keeping you dry and also to help a bit to ride over bigger waves. The cons are, they create hull slap when sitting still and thereby creating noise. Rolled chines are quieter when poling, but a wetter ride.


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## firecat1981 (Nov 27, 2007)

Yep, like he said. Has little really to do with lift, just helps to dry out the ride. Does create some slap, but not much more then any other hard chine would.


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## Blue Zone (Oct 22, 2011)

Mike,

Those examples you put up aren't actually chines. Chines are the point where the side of the hull meets the bottom of the hull. As mentioned above, they are spray rails and they seem positioned high enough on the hull sides where they will not be near the waterline at rest, so there should be no hull slap.

I wonder though if the reverse spray rails as shown might deflect chop too close to the boat thus creating a secondary source of spray?


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## pt448 (Mar 22, 2014)

Correct me if I'm wrong, Mike, but I think he's referring to the very bottom back of the hull where the sides meet the bottom and transom. It seems to me like they would help limit sliding in turns and maybe help the hull track straight. However, I admittedly know very little about the subtle details of hull design.


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## schwaggen01 (Dec 22, 2014)

@MariettaMike - The theory is that the reverse chines essentially "trap" water between them, creating a pad of higher pressure and thus allowing the hull to plane at a lower speed, as well as jump onto plane more quickly. The downsides come at the cost of maneuverability, both running and poling. A friend has one of those Cayo skiffs- I'll ask him what it's like.


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## CurtisWright (May 9, 2012)

schwaggen01 said:


> @MariettaMike - The theory is that the reverse chines essentially "trap" water between them, creating a pad of higher pressure and thus allowing the hull to plane at a lower speed, as well as jump onto plane more quickly. The downsides come at the cost of maneuverability, both running and poling. A friend has one of those Cayo skiffs- I'll ask him what it's like.


Yes, this nailed it. I built reverse chines in my fowl river 16 because I have a huge tunnel and needed extra lift to keep the stern from squatting. In fluids, the technical terminology is It prevents eddy current losses. It's the same principle employed on Airplane wing tips that have the up turn or flat plate on them. Also used in cupped propellers.


In turning on plane it keeps the boat flat and thus makes it slide, but my hull planes around 8kts even with the tunnel.


A minor benefit is spray deflection.


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## Otter (Sep 7, 2015)

Since you put a pic of Glassers skiff up I have a question or would like some opinions. It looks like his chines are a good 2.5-3". Would it make since to bring dead rise to the transom level with the chines to soffen the ride? Not critiquing his work. Just seems like it would have no negative effects. I would think the draft would be the same and would ride/handle better. Any thoughts?


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## Otter (Sep 7, 2015)

Or would this not be enough deadrise to make a difference?


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## MariettaMike (Jun 14, 2012)

Blue Zone said:


> Chines are the point where the side of the hull meets the bottom of the hull.


You can have a round chine at the bow and a reverse chine towards the stern.



Otter said:


> Or would this not be enough deadrise to make a difference?


It is my understanding that 2 degree dead rise gives enough structural benefit to prevent the bottom of the boat from deflecting "oil canning" and makes a "high center" so when the boat drags bottom you can still spin it around and go back to deeper water. (My Super Skiff is really good at that.) The ride really isn't any softer than a flat bottom until you get to 12 degrees or higher, but draft is increased 2" and higher.

I understand the reverse come benefit of lowering the spray, but I'm still missing any real world confirmation of a discernible benefit for planing efficiency/speed.

I am also concerned about effects on "spin out" like some have experienced in Whiprays while turning at high speed or side hopping like some over powered john boats will do. And am wondering if that is the reason they made the stepped chine towards the stern of the Cayo 173?


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## schwaggen01 (Dec 22, 2014)

@MariettaMike - You are correct concerning the deadrise/structural role.

In reality, a reverse chine will actually throw more spray than a square one, due to the water folding back into the trough. As Curtis Wright pointed out above, the real world benefit is a lower planing speed due to the reverse chine keeping more water under the boat. This is great, as long as you are going in a straight line.

One of the effects of a hard chined boat (and especially a reverse-chined one) is that in a turn, the inside aft chine experiences higher pressure as the boat tries to heel into the turn- acting almost like the flap on an airplane wing, pushing the opposite corner DOWN (the bow/outside of the turn) This means cornering very flat (in a boat as light as most skiffs)- which can lead to chine walking, or extreme bow steer depending on the design of the hull. This is the reason for the cutaway on the Cayo (the later HB Professionals have a similar feature) This relieves that pressure enough to let the boat get up on a rail in a turn (in theory). It does throw more water, but it's far enough back that this doesn't matter.

The spin out or hopping you describe is a feature of an extremely flat bottom- there's just not enough lateral resistance on the surface (Like a kneeboard, for example) Lateral strakes can help, as can reverse chines, but with the effects described above.


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## grovesnatcher (Sep 25, 2007)

schwaggen01 said:


> @MariettaMike - You are correct concerning the deadrise/structural role.
> 
> In reality, a reverse chine will actually throw more spray than a square one, due to the water folding back into the trough. As Curtis Wright pointed out above, the real world benefit is a lower planing speed due to the reverse chine keeping more water under the boat. This is great, as long as you are going in a straight line.
> 
> ...


Great explaination.


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## Backwater (Dec 14, 2014)

CurtisWright said:


> Yes, this nailed it. .......
> 
> A minor benefit is spray deflection.



By nature, throwing the spray down will create lift. But go to a mfg that has a boat that has lift strakes and ask what their purpose is. Cayos do not have them, only outside chines. Their center rails (like what you see on the bottom of a jon boat) are to keep the boat tracking straight and keep it from sliding on turns.

With a boat that has lift strakes, each strake is like a step to create lift once there is more opposing force created by boat speed. The reverse chines on the bottom of the freeboards are MAINLY to channel water back down. But again, it does create some lift, but that's not their main purpose. Your theory about cupping does not create lift, but just the opposite, it creates suction, just like your tunnels do in a tunnel hull boat. It's only the hard force where the water is thrown back down from the outside chines is where some lift is created. 

The purpose of the 2 most center lift strakes, in the example pic below, are to create a flat surface, big enough to ride on at higher speeds. Higher speeds need less surface (sort of the concept that barefoot skiers use). Each step also throws water back down, further creating more lift. The last liftstrake on the side edges of the hull, where someone here said.... "where the side edge meets the bottom" is called the chine. And yes, the chine provides some lift by knocking the spray down, but it's main purpose is to keep water sliding up the freeboard and thereby getting you wet on choppy days. It also digs in when turning to help grab the water and allow you to turn at higher speeds. 

So in example below, this setup is what s called for to allow a deeper "V" bottom to run on top of the water with less drag on the hull. Less drag = less hp required, faster speeds and less fuel consumption. Of course the advantage of the "V" hull design is to run in rougher water without beating you up. The cons are it takes more water to get up on a plane, takes deeper water to run, requires more hp and can't pole in very skinny water.











But skiffs like the Cayo by nature will not require much to get on a plane because the back bottom hull is nearly flat and that displacement alone creates lift, much like a wide jon boat. The rails across the bottom only purpose is to keep the hull tracking and keep it from sliding on turns.











This next image below is a semi-V hull design with wide outside chines with no lift strakes but a wide outside chine. The outside chine will help throw the spray out but because it's not reversed, the wind may catch the spray and throw it back up and on you. That wider chine pad works as a lift pad to keep this boat from sinking further down in the water. Boats with semi-V and V hulls will also ride softer than a flat bottom skiff hull and if that boat had no outside chine and a rolled edge, would be a quieter boat when sitting still, but a wetter ride.











In the boat business, each mfg is building a specific boat for a specific purpose

Also boat with wider sterns and/or centers will float higher and carry more weight, in nature due to the hull displacement but may require more hp to push them. Narrower stern boats, (even if the center beam is wider than the stern) will take less hp to push them but may not ride as high and not carry as much weight.

On that note, tunnel hull boats sit lower in the water and even ride lower since there is less hull displacement in the stern and also because there is a suction that is created by the tunnel. But it allows the motor to ride higher of course. BTW, I have a fix for you tunnel hull guys who notice their boats riding lower in the stern, not by adding more hull displacement (of course that helps but adds to the hp requirement) by eliminating the suction. 

Mike, all those pics above have built in spray rails/chines waaay up the freeboard. Those are to compensate for having less hull in the water when sitting still in the water. Less boat in the water = easier boat to pole. But the problem with having more weight forward in a narrow hull front, with no lift strakes (which causes additional hull slap when poling) is that the spray will ride up the front and up the freeboard, causing spray and water to come over the gunnels when running. Or worst case, is susceptible to spearing waves and submarining. That's why they have those overside spray rails which also acts as more hull displacement and lift if the boat spears waves. You will never see big water boats have them because they take care of that need in the hull bottom itself.


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