Tunnel hull shaft length

I’m needing some advise on a new setup. The plan is a 17/52 Alweld prop tunnel with a 40hp Mercury tiller. Wanting this boat to run as shallow as possible, so that leads to a few questions. If I do a 21” transom with a prop tunnel (4.5”), will a long shaft engine run with the skeg above the bottom of the boat? Or should I go with a extra long transom? Boat will have a hydraulic jack plate with the factory electric trim. Any advise is helpful. Friend of mine has a 17/56 xpress tunnel. I like his setup but he has remote steer and I’m a tiller guy. I’ll be ordering this boat as soon as I figure out what I need. Jets are out of the question so I’m gonna stick with a prop tunnel setup.

I have a jet tunnel 1652 with a 23" transom and I run a short shaft (15") jet and it sits almost 2" above the transom to tuck in properly. With your prop tunnel being taller, you would probably need a short shaft to sit 4-5" above the transom. I would think you want the tallest transom you can get even with a jack plate.

I’m fairly certain my friends 17/56 had a 27” transom and a 20in long shaft Yamaha. Just from fishing out of his boat there isn’t anyway a tiller handle would work comfortably. Maybe a 21” transom and a short shaft engine will work. Now gotta figure out if I can find a short shaft 40. Thanks for the reply.

I guess it depends if they measure the transom from the bottom of the boat to the top of the transom or the top of the tunnel to the top of the transom. I measure from the bottom of the boat to the top of the transom and it's around 23". From the top of the tunnel it would be around 20.5" and you can see my motor is mounted 2-3" above the transom. It could depend on the jackplate you get on how much rise it will give you. But even with a short shaft engine, you might need 5-6" of rise above the 21" transom to get the motor up behind the tunnel. I'm pretty sure the skeg will still stick down below the bottom of the boat either way. This looks like a situation where you need to talk to a lot of people to figure out what will work best. If you get the 21" transom and then need to run the jackplate all the way up, the jackplate is then worthless is you wanted it for flexibility of motor height. I've never dealt with a prop tunnel but I'll search around to see if there is any good information or pictures to help. And yes, it's not easy finding a short shaft motor so that might be the hardest part of your plan.

edit: It's tough to find good information and pictures on prop tunnel setups. I think with a tiller, it will leave your arm pretty high whether you have a 21" transom or 27" since the motor will be up to get the prop in the tunnel area. Here are a couple of pictures of different boats to show how high it might need to be. I can't tell if these are 20" (long) shaft or 25" (extra long) shaft motors

I’ve searched for anything I can find on and haven’t came up with much. That’s why I figured I would post the questions. I’m thinking the Alweld “mud” tunnel is 4.5” tall. I doubt Alweld measures from the top of tunnel to top of transom. So take a 21” transom minus the 4.5” for the tunnel, puts the cavitation plate on a short shaft 1.5” above the top of the tunnel. The hydraulic jack plate will give me 6” of lift and 2in of set back. I’m not sure what the prop diameter is, but this should be pretty close to perfect, right? Nobody has anything in stock, especially what I’m wanting. So between you guys and random internet pictures to figure it out. Lots of money to spend so I want it to be right. I don’t trust the dealers around here enough to help me as they mostly deal in high end bass boats.

This boat is mostly gonna be in deeper parts of the river, but If I’m gonna spend the money I want it 100% capable and setup correctly. Any information I can get is very much appreciated.

Finally got ahold of the guys at Alweld. They said they measure from the top of the tunnel to the top of the boat. So that makes things clear. On a long transom the long shaft engine cav plate will be level with the top of the tunnel. Now the question is should I go with a long or short transom boat. I’ll be buying the engine to match.

Yeah, that's good information to know. So it sounds like it's around a 27" transom to the bottom of the boat. That makes me think a long shaft might be what you need for that boat. If you do find a boat in your area, it sounds like you would want to do a test mounting of a 20" engine to see if that is correct before committing to buying something. Isn't it strange that you are ready to spend the money for the combination you want and you can never find anyone/dealer that can really help you out.

Apparently everybody is buying boats because of the virus, idk? I called a southfork dealer to get a custom boat made, spoke with him and never heard back. Called Gailen himself from southfork. He sounded like a good guy but after emailing him what I wanted and telling him I’m ready to get the boat build started. I haven’t heard anything back from email or by phone. Same with backwoods landing. So I’m waiting on quotes from the Alweld dealer. I guess this virus has everybody backed up. We will see. A custom boat isn’t out of the question, but I can’t get a call back. Hopefully the Alweld dealer will come through.