Sea Ox Tunnel

[Dipper]

I am considering adding a tunnel to my 20ft Sea Ox. In another thread a member suggested I post this here to see if JM had something that would work for me. Thanks in advance.

[TomW1]

It would take a lot of complicated calculations to design a tunnel that would work for your Sea Ox 20 because of the fairly deep V. If you have a skeg on the keel you would need to get rid of it as it would interfere with the water flow to the tunnel. How shallow are you trying to get. The 20 Sea Ox with no load has a draft of 8 1/2" according to the specs I found, that is with no motor.

Tom

[Dipper]

It doesnt have a skeg, 14 degree deadrise at the transom. My isssue is that there are a couple shoaled areas that are usually about 3ft but when the wind blows from a certain direction it can really drop. The boat will be loaded with oysters and/or gear so that wont help either. I have no run this boat loaded out so I dont know how she drafts now but I need all the help I can get getting to and from my farm. Couple local commercial fisherman have told me their tunneled sea oxs will run shallower than their flat bottom skiffs. Hard to believe I know but I trust what they say. Thanks for any advise and if you can talk me out of it I'd sure have alot less work ahead of me.

[fallguy1000]

It would take a lot of complicated calculations to design a tunnel that would work for your Sea Ox 20 because of the fairly deep V. If you have a skeg on the keel you would need to get rid of it as it would interfere with the water flow to the tunnel. How shallow are you trying to get. The 20 Sea Ox with no load has a draft of 8 1/2" according to the specs I found, that is with no motor.

Tom

This is what I was fearin. A lot of modification and you might get to 6", but way worse than an old pontoon you could skinny at 4 and load to 6 I think. The main thing about grounding is to come off. That would be easier with a pontoon as well. Vees dig in good.

[Dipper]

I see what you're getting at. So you think with the tunnel mod it would really only get me a couple inches shallower? The other thing I am thinking about is that if I build her all composite and then decide down the road to sell or repurpose as a rec fishing boat I may really shoot myself in the foot having the tunnel.

[TomW1]

Checking out some of Jacques designs similar to the Sea Ox around 20" there PPI is around 450 to 500lbs. So once you start adding the motor that will add an inch of draft, passengers and fishing gear and safety gear will add another inch of draft. Don't know how much gas and water you will carry but 6lbs for gas and 8lbs for water in bait wells can add up fast. So you could be looking at a total 3" of draft over the 8 1/2" for the boat alone.

Tom

[cape man]

There is a difference between draft at rest and when planing, and a tunnel is most useful to allow you to run across a shoal area, as the lower unit and prop are now running in a hump of water that is above the keel/bottom of the boat. All of the DPI numbers here and elsewhere are for a boat at rest. A tunnel will not significantly change the DPI, but will allow you to run the engine higher than one on a transom while underway.

[Fuzz]

If you need a tunnel to do the job then put it in and live with the downsides. I would look at how the commercial boys tunnels are built and do like wise.There times when an inch or two makes things go or no go. I spent a number of years commercial fishing an area where just a little less draft was gold.

[jacquesmm]

All the remarks above are correct: you can't simply graft a tunnel on a boat and expect it to work.
Yes, I use similar tunnels on several boats but all those hulls have about the same characteristics: flat or almost flat bottom, light weight, no strakes.

Keep in mind that tunnels have drawbacks, there is always a price to pay in performance especially in deep or moderate vee planing hulls.

[Dipper]

Thanks for the input guys. I'm still really on the fence as I am trying to decide if I go the composite route and worry about possible resale down the road or just go as cost effective as possible, pure functionality, add the tunnel and dont worry about resale. Ive been told that I can get a new similar commercial hull for a touch over 16k (no tunnel). Jacques, do you have a recommendation on where to get a molded tunnel or should I check with some of the guys that have them on their boats already and fab one myself?