General sportfish hull-tunnel design questions

[baeckmo]

If there's just one thing you should do, it is blocking off part of the top exit of the tunnels with a crescent shaped segment. Transverse width about 300 mm, height on top ~40 > 50 mm, reducing to 10 each end, and 50 mm long, outer shape to follow the tunnel roof, edges sharp. That will take care of the main ventilation path.

 

[Fiberglass 1 Inc]

I've never seen a 4" blade tip clearance in a tunnel before. We've worked on a couple of the 41's in the past and don't remember seeing that clearance before. As kapnD said, that is quite generous. Also, keep in mind that any large squared off trailing edge will create a low pressure area and any ventilation usually finds its way into that low. I know it seems counter intuitive but I have found tank test videos of little vortices traveling from the transom INTO a 30 knot stream of water flow and attaching to the rudders, causing total ventilation and loss of control (100 foot Navy mine sweeper, Carderock Institute). Your rudders have that large square trailing edge and are very likely pulling air in from the transom.

I apologize for possibly being misleading. After looking at another 41 and several other tunnel boats, 4 inch clearance is not unusual.

 

[Fiberglass 1 Inc]

I apologize for possibly being misleading. After looking at another 41 and several other tunnel boats, 4 inch clearance is not unusual.

Addendum - I was consulting on a Luhrs 41 a couple days ago and noticed it had the tunnel extensions and also had a prop tip to tunnel clearance of about 1.5 inches. This could be because it had more horsepower and therefore larger diameter wheels.

 

[brian eiland]

What ever became of this experimentation?

Also, do you utilize the vessel for sportfishing? just wondering.