Splash rail profile

[fallguy]

I’m looking for build advice on splashrails for my boat.

I need a minimum of 100, and as much as 200 lineal feet.

I have in stock and on hand about $1000 worth of 24mm corecell M80 foam in 4’x2’ sheets.

I was thinking about it and they probably need light 6 ounce glass on the exposed edges and so, a radius on the outside edge. Was thinking about gluing up 3 sheets of foam, then ripping 80mm wide and then ripping a triangle, then probably run a semicircle or some bit to make a radius (red).

Or any other suggestions. Maybe the corecell coated in epoxy is tough enough? Planning to bond to hull with 5200 after pieces are painted.

Not really a lot of time for testing, want to make it a best attempt.

thanks

 

[fallguy]

 

[fallguy]

I have 6oz glass and 1.5oz veil.

 

[TANSL]

The fiberglass must provide the necessary consistency to act as reinforcement or to withstand the loads acting upon it. The foam only serves to shape the splash rail and is not considered a structural element. This construction is normally used to create the top-hat-shaped reinforcements of any fiberglass hull.

 

[gonzo]

The spash rails are generating a lot of lift = force. They are a structural part of the hull. Years ago I added rails to a commercial lobsterboat. They were mahogany glued and screwed. They hit a breaker coming out of Oregon Inlet NC and it ripped a large chunk off. Also, because they stick out, the spray rails will hit a dock or pile so you should take that into consideration too.

 

[fallguy]

Fellas, thanks for adding to the constraints.

3m 5200 has bond strength similar to polyester or about 400-600 psi.

If I bonded them to the hull with epoxy, I quadruple the bond strength, but make the work about 10 times harder.

I have no mechanical fastener access.

If I make the bonding surface 3”, then each longitudinal inch has a bond strength of about 1500 psi. While there is a potential for the boat to come down hard on a wave, the weight of the boat would be about 11000 pounds directed over a wider area. Probably for this reason, the profile needs to be modified.

The challenge here is not to attack the bonding plan, but help draw a profile and a glass schedule.

If 3m 5200 is a bad plan, I can accept that, but might try it anyway.

How about this profile instead?

Glass with 1708..?

A bit less force on the rail, but perhaps some more mist..

 

[wet feet]

Do keep in mind that the boat may be moored next to wharves with rails and bolt heads that can snag protrusions as the tide rises and falls.

 

[fallguy]

Do keep in mind that the boat may be moored next to wharves with rails and bolt heads that can snag protrusions as the tide rises and falls.

Mostly kept on a lift.

 

[Barry]

Your profile on the left will throw water into the air and with wind in your face will end up on the windshield/deck etc
Also this profile will not maximize lift on the front of the boat

The profile on the right will throw the water down and maximize lift

How to build it is the question.

The force exerted by a fluid jet on a vane is calculated using the impulse-momentum principle: (mass flow rate change in velocity)
Velocity is speed and direction. If you maximize the direction change, you maximize the velocity change and hence maximize the force on the vane

 

[fallguy]

View attachment 207917

Your profile on the left will throw water into the air and with wind in your face will end up on the windshield/deck etc
Also this profile will not maximize lift on the front of the boat

The profile on the right will throw the water down and maximize lift

How to build it is the question.

The force exerted by a fluid jet on a vane is calculated using the impulse-momentum principle: (mass flow rate change in velocity)
Velocity is speed and direction. If you maximize the direction change, you maximize the velocity change and hence maximize the force on the vane

I did expect the iso tri would make lotsa mist.

I need help converting your theoretical message into meaningful numbers.

 

[Barry]

If you mean meaningful numbers to quantify the amount of lift for your application; this would be tough as the boat is moving and there is not a quantifiable jet stream, ie mass flow rate etc. But the concept is that if you can maximize the angle of inlet to the angle of exit for a given mass flow rate you will maximize lift. The biggest advantage for the downward exit direction is to keep the spray down back toward the water surface so the wind will not cause the spray to end up on the deck/windsheild. There will be an advantageous lift, but as I said, it would be hard to quantify. It will help the front of the hulls from digging in to waves

Easy to miss the angles symbols, theta and phi.

Force on fixed Vane.

 

[fallguy]

@Barry

I mostly want an idea as to whether I could try to bond these on with 5200 if I make them 3” wide. So was hoping to understand the force on the rail. I don’t see significant lift from these.

 

[baeckmo]

@Barry

I mostly want an idea as to whether I could try to bond these on with 5200 if I make them 3” wide. So was hoping to understand the force on the rail. I don’t see significant lift from these.

Barry's approach is relevant here, since lift is force. For a rough estimate: The vertical velocity of the water equals (2*g*H)^1/2, where g is earth acceleration (9,81 m/s) and H is the spray height. Say the water coming through the slot between hull and center body reaches one meter above waterline, then its base speed is 4,4 m/s.

Then estimate the flow rate, say the slot/fluid film is 30 mm and the fluid is entering over a length of one meter, ie 0,13 m3/s. Water density is 1020 kg/m3; the mass flow is 135 kg/s per meter length. Now that must be redirected from 4,4 m/s upwards to horizontal, resulting in 592 N per meter. This speed estimate is probably on the low side, judging from the images I have seen; as the force is proportional to speed squared, even slight speed increase hits hard. Recalculate as needed with updated values. I'd say you need rails 50 mm wide here. Don't go for 3", that will spell fastening trouble!

In addition: it may be tempting to gain some extra lift from directing the spray downwards, but it will generate heavy splashing. Generally, it has been shown (Savitsky, Koelbel and others) that the spray downangle should be limited to about 15 degrees.

 

[gonzo]

@Barry

I mostly want an idea as to whether I could try to bond these on with 5200 if I make them 3” wide. So was hoping to understand the force on the rail. I don’t see significant lift from these.

Are you fabricating rails with foam core and then attaching them to the hull? That would be a really difficult job. If you are attaching foam to the hull and then glassing over it, the bond will be poor.

 

[Barry]

Barry's approach is relevant here, since lift is force. For a rough estimate: The vertical velocity of the water equals (2*g*H)^1/2, where g is earth acceleration (9,81 m/s) and H is the spray height. Say the water coming through the slot between hull and center body reaches one meter above waterline, then its base speed is 4,4 m/s.

Then estimate the flow rate, say the slot/fluid film is 30 mm and the fluid is entering over a length of one meter, ie 0,13 m3/s. Water density is 1020 kg/m3; the mass flow is 135 kg/s per meter length. Now that must be redirected from 4,4 m/s upwards to horizontal, resulting in 592 N per meter. This speed estimate is probably on the low side, judging from the images I have seen; as the force is proportional to speed squared, even slight speed increase hits hard. Recalculate as needed with updated values. I'd say you need rails 50 mm wide here. Don't go for 3", that will spell fastening trouble!

In addition: it may be tempting to gain some extra lift from directing the spray downwards, but it will generate heavy splashing. Generally, it has been shown (Savitsky, Koelbel and others) that spray downangle should be limited to about 15 degrees.

Awesome calculations, thanks

A query: If you run across the comments of "Savitsky, Koelbel and others" suggest " a spray downwards should be limited to about 15 degrees" could you send me a link.
The math suggests the maximum is obtained at 180 degrees.

Certainly there will be a optimum, not maximum, of the difference between the inlet angle to the exit angle as when the return gets to be close to 180 degrees, that the Force component at 90 degrees to the center of the Vane reduces as it approaches 180 diminishes. ie normal force gained per degree of change