Venting a tunnel

[timoub007]

I believe that all of that data is in my thread in the builder's forum.
Here is the post in my thread that discusses the first time I ran it with the old tunnel and the vent. http://forums.bateau2.com/viewtopic.php ... &start=178

GF-16 with a modified interior, my first build so it is heavy too
I used the tunnel from the PH-15 plans (which I believe is the same as the XF-20 tunnel) however I narrowed it from 19 inches to 12 inches
I have always ran a 3 cylinder, 25 hp JohnnyRude on a CMC t/n/t jackplate

T

[Doug]

The vacuum in the tunnel does not pull the boat down or up. It affects how much water is sucked up into the tunnel (non engineering term) which in turn affects how high the water is coming out of the back and in turn how high you can run your prop which controlls how shallow you can run. An open vent reduces the vacuum, lowering the water level coming out and forcing the prop to run deeper but also reducing drag and increasing speed. If you have vent control, along with a jack plate, motor trim and trim tabs it's almost too many to play with.

[mikebro72]

post deleted

[timoub007]

Doug,

I'm not sure I agree with your last statements regarding where the prop height can be. When I closed off my vent my prop slipped a considerable amount more than with it open. This indicates that relieving the vacuum with the vent reduces the amount that the water going through the tunnel is aerated. My RPM's audibly decreased as the speed increased when the vent was opened.

Tim

[sds]

pmfji

Maybe the vent isn't aerating the water as much as giving a "release" along the top of the tunnel. This could make the stream flow with less turbulence.

$.02 from the peanut gallery ,
Scott

[Spokaloo]

Mike, no need to delete your post, I think it had good information, just that the physics needed to be further detailed.

E

[Oceola]

Here's another thread that talks about venting and goes a step further with power options, type, and location in and out of the tunnel.

http://2coolfishing.com/ttmbforum/showt ... ge=1&pp=10

[stickystuff]

I was in New Smyrna this afternoon watching the weigh in at the Fish Stock salt eater tournament. They had just about any type of shallow water flats rig you wanted or could not afford. One was called a Morgan. I had what they call a three step tunnel. the front approach of the tunnel was recessed slightly and had what i thought was two holes that vente the tunnel. then tapered up to the norm in tunnel design. Only this tunnel was more cone shaped. Link is here. They show a view of the tunnel but not very clear. Hull is similar to PH15. All foam w/kevlar. Kind of neat.
www.diamondsuzukemarine.com/Morgam.htm

[stickystuff]

Salt Water tournament. Redfish/Trout. Much many entries. Long waiting line to weigh in.

[dpurcell]

Hey Ken, I was there as well would have kept my eye out for you had I known you would be there. I was lookin' a bit at the Morgan's, I didn't like how huge the tunnel was, too much lost displacement, so didn't notice the tunnel vent. I maybe back there tomorrow and will check it out.
Donny