thoughts on spray/lifting rails

[bostonhatteras]

Rob the pressures developed by any moving vessel are considerable. if a vessel is on plane, the pressure developed is a function of the weight of the vessel opposing the ability to plane therefore a larger vessel at a given speed is developing more pressure than a smaller vessel at the same speed. as for the smart rail, my point is that the thin extrusion will not substantially add to lift becouse it will deflect. Dans comment about paint sticking to pvc is quite valid, I know lexan or phenolic plastics hold bottom paint.

[34Hatt]

Well if you guys did some searching here you would find posts saying that smart rail do hold on I even had a lift block shift and the strap was against the rail and it did not tear lose.
Also they hold bottom paint fine and I cruise 23-24 kts top out 28-29 kts. Even at that speed they don't deflect, they did do some R&D while inventing them it seems. I have had them on the boat for about 5-6 years now. No drilling, No screws just glue!

They did help with spray when I did them but I did not see a speed change. I had talked to Steve McPherson about lift rails on hatt's his reply was you can have two of the same boats and one will make a difference and the other one it won't! Guess it depends on loads and weight distribution.

[TopHattandTails]

Dan,
Interesting... What sort of wave action do they become useful / or waves become too big to keep her dry? I'd be interested in the spray rails purely for the spray factor, not the speed (but that would be nice too...). We usually have a 2' to 3' close chop on Lake Erie. Wave sets are real close together (2-3 second intervals). I'm probably don't care much about performance in anything over 5 footers - that's supposed to be interesting.

[34Hatt]

Dan,
Interesting... What sort of wave action do they become useful / or waves become too big to keep her dry? I'd be interested in the spray rails purely for the spray factor, not the speed (but that would be nice too...). We usually have a 2' to 3' close chop on Lake Erie. Wave sets are real close together (2-3 second intervals). I'm probably don't care much about performance in anything over 5 footers - that's supposed to be interesting.

Good question the answer is not a straight foward one because it all depends on were you mount them. Such as on my 34' I kept them low so with big waves the wave hit the hull above the rail!!! Yup they don't work so well then You will see some boats with them mounted half way up the hull and those work much better but can kill the look of the boat. We all say everything is a trade off here another one.
Mine did stop that little bit of spray on those nice days so I was happy, on those BAD days the boat is getting wet and that's not going to change

[Boatsb]

Spray rails are not Lifting rails and visa versa.

The lifting rails are lower and increase the hulls lifting area by adding surface and keeping the water pushing in the right direction.

Spray rails are located further forward and higher providing a diversion for the water going up the bow. I have seen one piece rails stem to stern but they seem to be a combination and most often not great at either.

[REBrueckner]

"...if a vessel is on plane, the pressure developed is a function of the weight of the vessel opposing the ability to plane therefore a larger vessel at a given speed is developing more pressure than a smaller vessel at the same speed.."

No such physics exists in this universe. gobbledegook!!!

"Spray rails are not Lifting rails and visa versa. The lifting rails are lower and increase the hulls lifting area by adding surface and keeping the water pushing in the right direction...;"

In many down east lobster hulls the full length "sprayrail" is used for spray delection at the bow and slopes down so the aft portion serves as a lift rail. A typical limitation is that the aft end has less surface area than a "lift" rail...so lifts less....

As has been discussed in earlier threads, consider a lift rail and trim tab about parallel on average to the keel bottom; for example, a 4" wide lift rail perhaps 20 feet underwater has a lfit area about 1/3 x 20 or about 6.7 sq ft....compare this with,say, a 2ft long by 3.3 ft wide trim tab...(huge) the area will be about the same, but the tab is all at the stern...so will lift the stern more due to better leverage...that is, more torque about the boat's center of gravity...effectively, it will be more efficient since a smaller trim tab area will provide about the same vertical torque.

[34Hatt]

The question was about Spray and the answer was about Spray!

So what is the last two post about???

[Boatsb]

Thats the example of the some of each not being the best of either.

[REBrueckner]

Since nobody seems to have mentioned it: Putting 10ft spray rails on my 48 YF with my own labor cost roughly a hundred dollars for materials six or eight years ago..roughly 2.5" width....a solid pvc rail plus strainless screws and maybe two tubes of 5200 for 10ft each side at the bow. The spray rail itself came in 20 ft lengths but I did not see much use for spray suppression for another ten feet each side.

[REBrueckner]

"The question was about Spray and the answer was about Spray!"

If that comment is relative to the overall thread, you better reread the title and the original poster statement...ain't no "payback" from knocking down spray!!!