Tunnel Hull help

[dearl]

I'm guessing you wanted a more complicated answer. Looks like you put a ton of work into your boat to drop a few pounds. I'm guessing to go faster and now it has your weight distribution jacked up. It looks like your motor is too high, maybe not. You need to be trimmed out so the jet nozzle is flat and pushing your boat forward not UP.

A few pounds is an understatement. All of the mods that were done were to shed weight, i need a hull that is light and drafts very little, Before the mods the boat was very nose heavy, took forever to get on plane, did not porpoise and had no spray coming over the transom and would run 33-36 mph with ease and drafted 6 - 8" of water. I could trim the motor to get it up to speed and she would tote the mail with no spray.

Now the hull is very, very light, sits on top of the water drafts maybe 4" jumps on plane and will hold it down to 14 mph top speed is 33 and porpoises very bad at that speed. The spray is unreal if you even think of touching the trim.

It is not hard to for me to beleive that with at least a 200 - 300 lb weight reduction that the boat would be faster than it was before,

I know now that the tunnel extension is the main culprit, its causing drag on the engine, plus the angle of the foot is catching the water coming out of the tunnel at a weird angle causing the spray. I have removed the existing transom extension, and plan to build a new one parellel to the hull with a adjustable spray rail, this should allow me to lower the engine on the jack plate, and adjust on the fly to get where it likes to run.

 

[handyandy]

Before you go through all the trouble of welding up the tunnel I'd keep messing around with motor height/weight distribution before you go through all that work. I can understand wanting to get rid of a tunnel, to me, and to you as well the cons of a tunnel outweigh the pro's. This is more so on flat bottoms it seems like. Wooldridge and few other of the northwestern boat builders seem to have the tunnels for outboard jets down pretty well, but their boats with them aren't a flat bottom like yours and are specifically designed for a tunnel. With that said if it were me I'd mess around with weight distribution more before I went through all the work of welding up the tunnel. The bags of cement or some other heavy weight that's easy to move around works well for experimenting before you actually move something like the batteries. I suspect you need more weight up front being you use to have heavy flooring throughout the boat that is gone now that helped weigh the front down apparently just right since you got 36 out of it before.

 

[dearl]

Before you go through all the trouble of welding up the tunnel I'd keep messing around with motor height/weight distribution before you go through all that work. I can understand wanting to get rid of a tunnel, to me, and to you as well the cons of a tunnel outweigh the pro's. This is more so on flat bottoms it seems like. Wooldridge and few other of the northwestern boat builders seem to have the tunnels for outboard jets down pretty well, but their boats with them aren't a flat bottom like yours and are specifically designed for a tunnel. With that said if it were me I'd mess around with weight distribution more before I went through all the work of welding up the tunnel. The bags of cement or some other heavy weight that's easy to move around works well for experimenting before you actually move something like the batteries. I suspect you need more weight up front being you use to have heavy flooring throughout the boat that is gone now that helped weigh the front down apparently just right since you got 36 out of it before.

I agree, Wooldrige has their tunnel boats figured out, and with that application it works great I'm In the process of designing a new tunnel extension, plus I'm going to move the batteries anyway, that's 100 lbs. I don't need on the stern. I was thinking when I did the mods that it would be too much weight on the nose, now that I have driven the boat, I know it can handle it and more. I don't want to much up there but I really think it may be enough to help keep the nose down once I get the drag issue fixed. I know some guys are thinking that's a lot of weight on the front, but believe me when I say the nose of this boat is super light.

Before the mods, I had 2 batteries, onboard charger, and a 40 gallon live well under the front deck, all construction was with .125 plate and with me @ 215lbs. that was a lot of weight. and it would still run like a scalded cat.

Now the nose, as lite as it is with only a 19 gallon fuel tank, and me, my son, and everything else In the boat on the front deck, it wants to stand straight up In the air @ 33mph.

Some pics of the destruction process, I got to clean the old welds off, doesn't help I built the old extension out of 3/16 aluminum plate.

 

[dearl]

Got the old welds cleaned off, mocked up the new tunnel extension angle with a piece of angle iron, set the shoe were it needs to be with the jack plate, looks like I should be able to drop the motor down a couple bolt holes on the motor. I'd like to have it set at full extension, the shoe is were it needs to be with no risk of placing the shoe on top of the extension. By the tape the extension needs to be 9.5 -10" long? I plan to use UHMW stock to make the top of the extension adjustable. Also I'd like to extend the extension from the bottom of the 45 degree drop all the way under the pods to the sides of the boat, trim tab so to speak. Any thoughts?

 

[handyandy]

I'd just make the extension first see how it does before making the trim tab type things. Keep the changes one at a time now to see what effects what.

 

[dearl]

Got the new extension welded on this weekend, after all was said and done, it ended up being 9.5' long and parallel to the hull. I cleaned every thing up last night and took a lot of pictures from different angles so you can see what's going on. I still have to add the UHMW stock to the top and bolt it down for the adjustable plate, and raise the motor up to the last bolt hole. This should put the front roll pin even with the plate with the jack plate all the way up and motor tucked in. Let me know what you guys think.

 

[redrum]

Interesting looking tunnel. I've never seen one extended like that to compensate for a jack plate. It's like the spray plate and tunnel are combined. I'm interested to see how it works. It seems like that semi-circle cut would create an awkward vortex with the water feeding the pump.

 

[gabeskillzz05]

Eager to hear how this works. Once you get it dialed in I'll bring my boat down so you can do it to mine!!! :lol:

 

[dearl]

I spent yesterday afternoon moving the motor up to the last bolt hole, and making the adjustable tab for the tunnel extension. It looks perfect, height is good (I HOPE)! I used a piece of .080 aluminum for the tab for now, cant find 1/4" uhmw around here so I'll order a piece and replace the aluminum later. I know if the shoe touches the aluminum all I'll hear is a rattle. Plan to take her out today for a test run, I'll post results for you guys tomorrow.

 

[dearl]

Took the boat out yesterday, I like the way the boat feels with the new plate. I have more control of the throttle now, the spray is gone completely, but It still wants to porpoise at WOT. I know now that I need to distribute the battery weight to the front. I did pick up some speed, top speed was 34.4 but I had to let her bounce a little to get up to that. She's got a few mph left in her, once I can play with the trim without the porpoise I believe she'll be perfect.

 

[mphelle]

In my opinion, the floatation pods are mounted incorrectly, causing the porpoising. I would remove them and move the batteries to the front compartment. I would also lengthen your prototype flap since I think you will find yourself trimming up more.

 

[dearl]

In my opinion, the floatation pods are mounted incorrectly, causing the porpoising. I would remove them and move the batteries to the front compartment. I would also lengthen your prototype flap since I think you will find yourself trimming up more.

Not understanding what is incorrect about the way the pods are mounted.

Started the big battery move this weekend, gutted the front end to install 2 new battery mount pads, got those welded in yesterday. Batteries are re-mounted, just about done with the re-wire, will begin installing the front deck and hooking everything back up. should be ready for a water test by Thursday. If nothing else it will draft less on the stern now, 2 batteries and an onboard charger are pretty heavy.

 

[mphelle]

Battery project looks good, you have a lot more energy than I do. Your pods were mounted high by someone who thinks keeping them out of the water while on plane will reduce drag. In your case when you try to raise the bow with trim, the pods tip down catching the water and forcing the bow back down, and so on.



Others, including Beavertail, think the bottom front on the pod should be flush and smooth with the bottom and angled up about a half inch in the rear to allow some trim. Ranchero50 had similar issues with his pods and used an interesting solution to porpoising. https://www.tinboats.net/forum/viewtopic.php?f=83&t=8385&start=240 about halfway down the page

Your pods have the wrong angle to just move them down, which is why I suggested removing them to test the porpoising theory.

 

[redrum]

Nice work. Do you have hatches on the deck to access the batteries? Is that area in the center for your fuel tank? Are those your TM batts? Do you still have a start battery in the back? Hope it works out for you it's frustrating putting a ton of work into something and it not working out.

 

[dearl]

Well I got a lot done last night, pretty much buttoned everything back up, still have the fuel fill to install and the front deck hatch. I plan to bleed the steering today while my son is there, that process takes 2 people, other than that, should be ready for a water test Wednesday.

Battery project looks good, you have a lot more energy than I do. Your pods were mounted high by someone who thinks keeping them out of the water while on plane will reduce drag. In your case when you try to raise the bow with trim, the pods tip down catching the water and forcing the bow back down, and so on.

View attachment 5

Others, including Beavertail, think the bottom front on the pod should be flush and smooth with the bottom and angled up about a half inch in the rear to allow some trim. Ranchero50 had similar issues with his pods and used an interesting solution to porpoising. https://www.tinboats.net/forum/viewtopic.php?f=83&t=8385&start=240 about halfway down the page

Your pods have the wrong angle to just move them down, which is why I suggested removing them to test the porpoising theory.

And this makes sense....Once I get it back on the water and test it out, if I still have the degree of porpoising as before, I will play with the pods. I can drop them down if need be, probably have to customize the pods but it can be done.

 

[dearl]

Nice work. Do you have hatches on the deck to access the batteries? Is that area in the center for your fuel tank? Are those your TM batts? Do you still have a start battery in the back? Hope it works out for you it's frustrating putting a ton of work into something and it not working out.

Nothing in the back now, everything is under the front deck. I plan to order 2 new hatch's for the front bulk head to access both batteries.

 

[mphelle]

Crazy fast progress, if you used a video camera it would be better than most cable shows. If you have a GoPro or another waterproof option, hang it off the back during your test.

 

[dearl]

Got everything back together yesterday, bleed the steering, and took it out for a test run. Wow! moving the batteries made a huge difference. No more spray, better draft at idle and porpoising is all but gone. I mean I can still make it porpoise if I trim it to the moon but it ran incredibly well. Boat jumps out of the water, planes very easy and hit 33.7 and would hold there without jumping. I could probably get it a little faster if I would have played with it more. I do believe the pods are holding me back from hitting 35, but if I remove them I'll lose my draft at idle and I'm not willing to do that. I got a couple of videos I'll try and get posted later.

 

[rotus623]

Running 8mph more with a 90/65 is probably about right, when comparing apples to apples. I wouldn't expect to get too much more out of it. I had a prop 75hp on a 16' aluminum boat and it would max out at 36mph with a light load, trimmed out. Just food for thought here.

I dont buy it, 33 is not about right, like I said earlier I have had this boat up to 36 when it was 200 lbs. heavier.

Just sayin.......

Either way, boat looks great. I love the console on the casting deck and would love to see some side shots!

 

[handyandy]

75hp on a 16ft aluminum and only 36 that's not very good something wasn't right either set up or prop. Friend has a 3/16 thick 2060 with a 1979 70hp johnson we get 36-37 out of it when it's just us and fishing gear in it. It goes down once it has the big duck blind on it, decoys in it, and couple more guys hunting.