Alim Marine tunnel boat rebuild

[kapnD]

I’m looking for a lot of water traveling up the outboards leg at speed.
Thinking you may still need to block off some of the tunnels height, will reduce drag, improve performance.
If filled with foam and glassed, you’d also get improved flotation at the stern, resulting in less backwash on deceleration.

 

[Frans old man]

Sounds like a good idea. At the very moment, I'm just trying to get it to plane off. Thanks though, hopefully I can just get back to work. Spring fishing is starting to pick up here, and my bride is kinda over this project.

 

[Mr Efficiency]

Gawd, that was quick !

 

[Frans old man]

Lmao.....well, ya see what happened was.....I didn't have much to do today....and it was a pretty day.......and my wife said to get off my arrssss. So, I got the tape out, took a few measurements, had a few smokes and contemplated a while, and said to myself, self, we can't use it like it is, so I got to it.

 

[Mr Efficiency]

kapnD may be right, you may get the leg drag he speaks of, but as you say, first you have to determine what height is too much, or enough. at least in the cut-down configuration you now have, the "suction" effect on the water flowing into the prop, will be much less.

 

[Frans old man]

Yes sir, I agree. But as I've said before, she is a dry boat with ample scuppers. Did not start out looking for performance or perfection. I just need function. If things are too terrible, adjustments can be made, as long as I can get back to work. Fishermen can't make a dollar if we can't get on the water. Rock fish are running hard in the sound right now in numbers we have not seen in 10+ years. When they have come in bigger numbers like this, the other marketable fish we can keep are soon to follow. Tomorrow will tell the tale about where I'm at in the functionality department. I'll update after the test ride.

 

[Frans old man]

Ok, seatrial was a great improvement, and now I can get back to work. A huge sincere thank you for all the input, help and advice.

The results were fantastic from my perspective. She didn't "plane off", but was able to make 18 mph GPS with a 10 to 15 mph headwind. So, I'm satisfied with that. All the speculations imputed are correct. Lots of water up the leg if the outboard, but not unmanageable by the scuppers. Outboard hieght is still not correct, too low, I think. And could use so.e venting in the tunnel. All that, I can tend to when time and weather permit. I'm going back to work, and using it loaded, will give me a feel for any mods next. The first of which will be the venting as the stern seems to be pulled downward al the time.

Again, thank you to all for your help. Nice to have a place where some competent, kind people willingly help one another. God bless you all.

 

[Mr Efficiency]

Well, I am glad that at least it is now useable, if you made 18 mph then the suction issue is out of play, if there was a "fountain" caused by the leg, it would appear to be too low, if possible raise the engine in small increments, when you get a chance to do so, it actually does not take much to make a difference in that regard. Alternatively, you could install a fairing ahead of the leg. But since you want to keep draft low, perhaps raising it slightly is the the better plan.

 

[Frans old man]

Hello all. Just a quick update on my tunnel issue. After a few seatrials, and a whole lot of research and contemplating, I've decided to cover the tunnel area with a flat area underneath and reform the stern area. Trim tabs, stingrays hydrofoil, and a couple other hair brain ideas may or may not work. My simple conclusion is, I'm trying to compensate for something that is missing from the hull. That being said, I've decided to buy a correct length shaft outboard and quit trying to make the boat do something it just will not do. So anyway, thank you for all the thoughts, ideas, and advice. I should have followed my gut in the beginning and closed it up from the start. Thank you all.

 

[Mr Efficiency]

So what happened, what problem(s) did you encounter with the lowered engine position ?

 

[Frans old man]

The console is mounted 11 ft from stern. At the 18 mph speed, she stood up so high, I could not see over the bow and I'm 6'1". Even tried putting a 30 gal drum of water in the very front of the bow. Had to tie it there or it would have crushed the console. You have to see in order to drive. To me it's a visibility issue which makes it a safety problem.

 

[Mr Efficiency]

With the motor trimmed right in ? Sounds like trim tabs are needed. If the engine isn't creating a fountain around the leg, I don't think I'd be worried about filling that cavity.

 

[Frans old man]

Trim tabs are definitely the easier way. I am going to make them fixed with a tunbuckle adjustment. I am trying to find a happy medium for this thing without having another gadget to think about and worry with amongst everything else while I'm working. My only thought is, if I lower the bow with trim tabs, that will raise the stern. The stern raises, and the prop will probably ventilate again. Just my feeling from what I've seen happen on the boat so far. So, to me its seems like a back and forth battle. Where as, if I put it back like it's supposed to be, I eliminate what's causing the issue, and set it up like a "normal" boat. That's just my thinking. I haven't made a decision one way or the other. I will say, the outboards I'm looking are 100 lbs lighter, which would give a bit more for scupper hieght at the transom. So, this is my thinking, and my options. Contemplating which way to go is all.

 

[Mr Efficiency]

OK, so the outboard is not ventilating or cavitating at present ? And the outboard leg is not dragging through the water creating a spectacular water feature ? In that case, you have made progress. There is nothing wrong with the turnbuckle idea, I recall making a couple of temporary tabs from 1/8" galv steel years ago, no hinge, just a small radius bend, and the sides and back turned up up about an inch to stiffen it. No problem once you get it set where it worked OK. This is a rough idea of what I did, err on the side of making it wider.

 

[Frans old man]

So, maybe not such a bad idea after all then. And yes, no venting, cavitation that I can tell. Only small amounts of water coming up the leg. Nothing crazy. It would save a great deal of money by adding the tabs instead of a new outboard. Mr.E, that was pretty much the idea I had for the tab design. I planned on using hinges as I have substantial stainless hinges, about 3.5 or 4 inch wide ones. The tab size I had in mind were 12" wide by 7" deep with the seven inch edges turned downward an inch to help increase the effectiveness. I'm just wondering if I lower the bow, raising the stern, if that would elevate the prop into the turbulant waters of the tunnel and cause ventilation again? I have no more room to lower the outboard mount, as the deck level and the hieght of the tunnel roof are approx 1.5" apart. That's really my biggest concern. At that point though, I wouldn't have a choice but to get a longer leg outboard. Maybe the last thing to try before such a drastic change.