Bulbous bows

[pee wee]

That's a lot of spray coming off the bb, but it's when it hits the hull and deflects outward and upward into the wind that it becomes a problem. Ideally you'd treat it as near the source as possible, but a spray rail on the bb might cause yet more problems. I doubt you want to experiment with different shaped bulbs at this point (although you could clad it with an outer shell), so my vote is spray rails on the hulls.

[OrangeQuest]

Question is, and I am not sure at the moment, is the hull a planning hull, semi displacement or only displacement?

From the short video FG posted, it looks as if bulbous bows are not pushing the bow up for it to be a planning or semi planning. seen other videos of power cats and those with bows like FG's, before the BB where added, seemed to ride with the bow a little out of the water but they were 42, 50, 70 feet boats too and all inboards.
There was a video of a power cat with a bow shaped similar to FG with the BB. They had spray rails but still a lot of spray that I am sure a cross wind will pick up.

I think if the bow was first designed to not only part the water but put downward pressure to lift the bow as speed is increased then the bulbous bows need to be tweaked to do that too. If that is not the case then need spray rails on the upper side of the BB to redirect all that water coming over the top of the BB.

[fallguy1000]

Question is, and I am not sure at the moment, is the hull a planning hull, semi displacement or only displacement?

From the short video FG posted, it looks as if bulbous bows are not pushing the bow up for it to be a planning or semi planning. seen other videos of power cats and those with bows like FG's, before the BB where added, seemed to ride with the bow a little out of the water but they were 42, 50, 70 feet boats too and all inboards.
There was a video of a power cat with a bow shaped similar to FG with the BB. They had spray rails but still a lot of spray that I am sure a cross wind will pick up.

I think if the bow was first designed to not only part the water but put downward pressure to lift the bow as speed is increased then the bulbous bows need to be tweaked to do that too. If that is not the case then need spray rails on the upper side of the BB to redirect all that water coming over the top of the BB.

Semi-displacement.

Rpms too low. Video at 3100-3300..

Standing up there is 220 pounds forward and maybe a 5cm draft change.

[glossieblack]

Will FG seek to correct the problem at source by installing spray rails on the bulbs, because an unacceptable percentage of spray to the windshield is coming directly from them?
Is FG currently sea-trialling experimental spray rails on the bulbs?
Stand by. Time will tell.

[fallguy1000]

My attempts today were a massive failure.

I did a rough fairing and at about 2800 rpms, the water comes off the bb in 8x11 sized pieces like paper.

There was so much water at 4500 rpms the wipers could not keep up.

[fallguy1000]

Will FG seek to correct the problem at source by installing spray rails on the bulbs, because an unacceptable percentage of spray to the windshield is coming directly from them?
Is FG currently sea-trialling experimental spray rails on the bulbs?
Stand by. Time will tell.

The BB is underwater, so u tell me where the spray rail would go...

I am thinking maybe I need to get them up above the water more..

[fallguy1000]

https://youtube.com/shorts/UZ6ALIRqG5Q?feature=share

[Jaysen]

I’m assuming that as you speed up, the sheeting gets steeper, moves aft, and eventually reaches up to the deck/windscreen. Based on the video I’m not sure you can solve this with rails on the hulls since it’s the top of the bulbs that are send up the spray.

The two thoughts I have are:
1. Is the top of the bulb sharp enough?
2. Maybe a narrow deflector right on top of the bulb. Think an arc to the outboard side the pulls the spray over the top. Think #1 but sharpened to the outboard side and rounded on the inside. Not sure that makes sense.

Edit: tried to make a pic of #2. Port bow looking aft. The red part…

[mhd]

I feel for you mate. A total pain.

I've watched the video a few times and looked at the previous shape compared to this one. The one observation I have is it looks to me that sharp edges seem to be prone to creating spray rather than reducing it - I also don't think that something under the waterline would help much (mainly as I assume that as you increase revs the bow will rise up out of the water anyway).

The closer something is to a sphere the less likely that is to create spray - smoother, less angular (submarines have pretty much spherical bows - for pressure reasons yes, but also less acoustic noise/turbulence as the water is shifted aside). Most hull shapes for the boats we build can't help spray and so try and deflect it away if it becomes necessary.

Bulbous bows on tankers etc., are more spherical in shape rather than sharp edges - i.e. bulb shaped. I know that isn't exactly the same thing at all as they are slow displacement hulls, but to my mind something less angular *might* help. That is not a suggestion, but it is my gut feeling. To remove all edges as much as possible - particularly on the leading and top edges - get away from the "diamond shape" (that you needed for strength) and make them more bulbous. I'm not the one doing the work though. Does that make any kind of sense? I could sketch something if it would help?

Also look at the top/side edges of the Aquila 70 you posted elsewhere. They are very rounded, not angular.

Good luck with whatever you decide.

Mick

[glossieblack]

My hunch is a T section with the cupped top of the T having a slightly larger footprint than the bulb below it, at a height around the upper red line in the pic you posted earlier.

In other words, the top of the T section to carry forward as far as the bottom red line, but at the height of the upper red line.

The spray needs to get clear of the bulb then be deflected down.