Splash rail profile

[baeckmo]

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

Oh yes, you're correct about the deflection for maximum lift and it might be ok for rails in the tunnel. But if you succeed in turning the flow 180 degrees, the spray film will hit the surface with the maximum velocity, which will generate a lot of "secondary" spray, making for a wet journey. I'll dig into the litterature sediments and come back with ref..; will take some time, now the grandchildren are filling the house for holiday celebrations......

 

[fallguy]

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.

After the exchange between Barry and Bodo, the plan is fairly clear for a flat bottomed rail that will be at some angle slightly downward, and I will reduce the dimension out to 50mm as per Bodo. What I want to attempt is to make the bonding surface 3” AND I am hoping to bond with 3M 5200.

Bonding the splash rail to the hull using glass and foam is very intrusive at this point in the build. The paint is 2 part polyurethane and very strong bond to hull.

If I build a triangle with base (hull) dimension 3” and outward dimension 2”, then bonding more conventionally would be so invasive. You’d apply the foam splash rail, then tab it to the hull top and bottom, then tons of fairing top and bottom and per Bodo and my plan, about 160-200 feet of work. It would take 2 weeks at least, probably a month to sand the locations, bond the rails, tab, fair, repaint with lines in the paint. The strength would be significant.

The faster way would be to prefinish the rail and simply bond it on with 5200.

I use some of Bodo’s numbers and help from chat gpt; see following comment.

 

[fallguy]

velocity (up) = 4.4m/s (probably less as not going up a meter if it hits the rail (see bulkhead drawing)

velocity (forward) = 24kts max or 12.34 m/s

v (combined) = square root of combined squares = 13.09 m/s

pressure = 1/2 • 1020 • 13.09^2 = 87kPa = 12.62psi

bond strength of 5200 is 380-500psi

force over 12 inches of 2” area is 24 • 12.62 psi or 303 pounds


Now, this math suggests bonding with 5200 is more than sufficient, but the intuition is not working for me that a 3” bond is 1000-1500 psi and 100 times stronger than the water pressure.

What am I doing wrong? I even added the boat speed to the calc.

I think using a full meter of vertical distance is a bit much..touche’.

 

[fallguy]

The hull is 13.4 degrees from vertical, so a 90 degree angle coming off it is angled downward same.

 

[fallguy]

I’m gonna glue them on unless someone makes a compelling argument against it.

 

[Ad Hoc]

.... Generally, it has been shown (Savitsky, Koelbel and others) that the spray downangle should be limited to about 15 degrees.

Indeed....we use a negtaive 5 deg for these applications:

 

[gonzo]

You should consider the stress on the skin. The laminate may fail by the skin separating from the core. I doubt it was designed to have a pulling force on it. Fasteners with backing plates could be a solution.

 

[Barry]

Some interesting spec sheets on Permabond.com. Adhesive strengths upwards of 4,000 psi. Looks like some of them are mixed in the nozzle when applying.

 

[fallguy]

You should consider the stress on the skin. The laminate may fail by the skin separating from the core. I doubt it was designed to have a pulling force on it. Fasteners with backing plates could be a solution.

Valid. The shear strength of the corecell foam is roughly 150psi, so while less than the bond strength, it is still far more than the force of the water.

Good callout. Thanks.

While I’m at it, I ought to do same for the coatings, but epoxy paint and 2 part polyuretha mbe bonds are also very strong, without even checking the values.

I think this means a splash rail failure is going to probably tear foam unless one of the paints has a poor bond through the coats.

 

[wet feet]

Some interesting spec sheets on Permabond.com. Adhesive strenghts upwards of 4,000 psi. Looks like some of them are mixed in the nozzle when applying.

There are several bonding agents that are supplied with mixer nozzles.Plexus and Crestabond come to mind.What might be the greatest challenge with making these pieces off the boat would be establishing the correct bevel and curvature of the inboard faces and maintaining it while covering with glass.Once skinned,there will be little flexibility and thus not much chance of adjustment.

 

[fallguy]

I’ve decided to buy a 12x48” piece of G10 0.25” thick and make cutting plates on the bow above the bow extensions, but this is above the waterline.

I will do these first and test, need about 4 weeks though; other things in the way.

I think the splash rails are still going to be needed.

The water is probably creeping along the extension as well, see pic.

There are several bonding agents that are supplied with mixer nozzles.Plexus and Crestabond come to mind.What might be the greatest challenge with making these pieces off the boat would be establishing the correct bevel and curvature of the inboard faces and maintaining it while covering with glass.Once skinned,there will be little flexibility and thus not much chance of adjustment.

true, but I think if I can build them flat; it’ll work

 

[fallguy]

I finally completed the move to Texas and I want to get started on the splash rails.

The current profile plan is for a triangle shape 3” long for adhesion to the hull, and 2” outward.

The outside edge is to be fiberglassed. To do so requires a radius of about 3/8” to 1/2” so the glass can travel around the edge. Also, to vac bag this profile would require standing the part up off the table a bit, here I digress from the query.

By putting a radius on the outer edge to deal with a manufacturing requirement, am I going to be creating a pathway for the water to continue upward?

Does this edge need to be reformed to the triangle?

I will add a drawing later today.

 

[Skip Johnson]

After glassing the triangle you could dam up one side of triangle and fill in with silica/epoxy paste.

 

[fallguy]

After glassing the triangle you could dam up one side of triangle and fill in with silica/epoxy paste.

Yeah, but I gotta build like 160-200 feet of it..

 

[Ad Hoc]

....The outside edge is to be fiberglassed. To do so requires a radius of about 3/8” to 1/2” so the glass can travel around the edge. ...By putting a radius on the outer edge to deal with a manufacturing requirement, am I going to be creating a pathway for the water to continue upward?...

It can do if not positioned correctly.
Make sure you have a minimum 5 deg downward angle (-ve) from horizontal.
This will encourage the flow to be downward and not to attempt to stay attached and go around the rounded apex.