Vent placement on stepped hull.

[Bob Rosa]

I have built a 25 foot hull with a 2.5 inch step 15 foot from the bow. Ready to install two vents and not sure of exactly where to cut the holes? Boat can be seen on youtube at Rosas Creative Works.

 

[montero]

I would move the step forward.

 

[Bob Rosa]

Sorry it's a bit to late for that. Step is where it should be per John Hacker design.

 

[fallguy]

Seems if Hacker Design did the original work; they ought to offer the vent spec.

If it was designed without, then my dime is to find someone competant to run the boat through cfd software.

It is possible, I am overthinking it. But it seems rather odd vents are not already part of the hull shape….

 

[fallguy]

Okay, so I found the link to the videos.

It appears you have already built the hull, so integral vents are no longer possible.

We have an expert here that may offer you some alternative if he sees the post or maybe not needed?

 

[Bob Rosa]

Interesting point you've made. I may be over thinking the need for these vents. CC had them on their step bottom racer hull. I also met a chap at the Travers City boat show a couple years back that had a similar design hull and found he needed the vents added to break the vacuum when running at speed.

 

[fallguy]

The smartest guy here might be able to offer you some guidance on thru hull vents on the step riser that are more active if you get him to post. It is not me. I would not know where they go even for best results. Only offering some chatter to keep your thread active.

I would probably add vents as a last resort because you are holing below the waterline to do it. As a builder, I recommend creating access when you build the sole if you find it a problem. It might be good for you to offer a photo of the step outside and inside for any of the professionals to offer best advice. Those guys are not gonna want to watch all your vids hoping for a shot of the step.

 

[Barry]

I was under the impression that the step continues to the side of the boat and would normally be vented on step

 

[Bob Rosa]

Thank you fellows for your input. The step does go all the way to the sides. I'll try to post a couple of photos. I have seen a design where a notch was designed into the side of the hull to vent the step. I considered doing this and still could. It's just wood and epoxy built. I did purchase two really nice Stainless steel Rod holders that could be used in the bottom as vent tubes. These have a very nice weld between the tube and the flange so they would be leak proof. The flange is of minimal height so it would fair in nicely to the bottom. The tubes are about 12 inches long so the open end would be well above the water line. The reason for my post is it seems to me, if these were placed to far aft of the step, they could catch water and give me a good soaking, while under way. The step is the frame directly below the steering wheel which is right where the feet go. I could not find a good bottom photo of the step.

 

[fallguy]

I recommend a picture or two of the outside of the hull. One further back and one closer up. I’m having a hard time making sense of the views offered and it looks like the step is down aft and not up, so I am all confused.

It could be upside down or rightside up, but would be good to see it in situ.

The inside picture is not much, at least for me. A NA might have a better go of it, but outside hull pic would be best.

Sure is a gorgeous looking ride.

 

[fallguy]

Assuming that is the bulkhead, then it is just the interior picture I am struggling with. I don’t see how a perpendicular BH offers any passive venting, so wait and see if you get some better answers during the week and also try to get a pic of the bottom, although it is fairly intuitive once the BH is seen. The interior pic just looked backward to me like the hull steps down, but it is just an illusion.

I don’t know that the rod holders are right; that seems like perhaps too large a hole 2”?, but I’m guessing 100%, so pay little attention. I’m thinking more on the lines of clam shell vents running into 1” tubing or something, then the faster you go the more air dumps…still guessing though.

 

[Bob Rosa]

Sorry about that. I will take some new photos latter today and post them. It is LS 6.2 powered about 430 hp. We are currently hosing and wiring. Plus installing a Performance Design intake with injectors and a Holly control system.

 

[Bob Rosa]

The step is aft up like it should be. A 12 foot straight edge was used to insure the aft 4 foot was in plane with the 4 foot just fore of the step. I'm hoping it does not hop like I've seen others do.

 

[fallguy]

All of your queries are beyond my abilities to help. All I can do is help get a clearer idea of the goals. The pros here probably understand hop and venting and give them some time and help them with details.

Do you have any plans for trim tabs or any means to trim? Others may inquire..

All the best, it is really a beauty.

 

[Bob Rosa]

here are two new photos of area for vent placement.