# Alumacraft 2072 tunnel / porpoising



## 4xsthefun (Jul 16, 2010)

I just bought a Alumacraft 2072tunnel with a 130 etec with a 19 pitch 3 blade prop and I can't trim at all at wot. If I try to come up at all on trim it starts porpoising bad. I have to leave the motor all the way down killing my rpms and speed. Turning 4600 @ wot at about 43 mph. When I try and trim the rpms come up a bit but I can't leave it up. This is a brand new boat and pretty aggrevating. Any suggestions would help. Tanks


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## KellyJoe (Apr 3, 2011)

Fighting the same thing with a VB 1650 T Alumacraft tunnel. Running a 50 Yamaha w/ a 4 blade stainless on a hydraulic jack plate. Not sure of the pitch but interested in the comments you receive. I added an aluminum hydrofoil hoping it'll help. With the sponsons off the back there's nowhere to mount any trim tabs to help. Good luck.


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## 4xsthefun (Jul 16, 2010)

*alumacraft*

The dealer assures me a 4 blade prop will fix the problem and has one on order for me to try,if it does help they will swap it for the 3 blade. I was also thinking a jack plate may help, but you are running both 4 blade and jack plate and still having issues does not sound good. I have also looked at the smart tabs, but where would you mount them with the sponsons? I have emailed alumacraft to see if they had a solution the problem.


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## KellyJoe (Apr 3, 2011)

Yeah I'm afraid the smart tabs won't work with the sponsons. The jack plate gets it up and helps with less drag and maybe a little more rpm's but I, just like you cannot trim out hardly any at all without porpoising. Thinking I may try to move my cranking battery from the rear to up under the console.

I called Alumacraft and they said that the trailing bottom edge of the transom is intended to be used as trim tabs. The bottom of the hull that sticks out past the transom. They are supposed to be bendable and should have been set up by the dealer. Alumacrafts response. Going to try out the hydrofoil in the morning and will post up results for you. Crossing my fingers.


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## 69RRVERT (Sep 21, 2006)

I had the same problem with my Alweld. I had trim tabs made from a piece of 1/8" aluminum plate and welded them to the bottom edge of floatation boxes. They are the width of the box X 3" wide. I can trim the motor until it stops and it will not porpoise. Thanks, Steven

Pics:
http://2coolfishing.com/ttmbforum/showthread.php?t=301931


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## Rodster71 (Mar 30, 2010)

I have a 2004 Alumacraft 2072 tunnel with a Yamaha 115 4 stroke. Does the same thing cause of the rear pontoon steps. It's designed to take off in shallow water but hurts when running.


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## ROBALO23 (Jul 7, 2011)

Id try the ole sting ray hydrofoil from Academy. I have a 23 Robalo with Yammy 225 four stroke . Sting ray eliminated all porposing and bow rise during take off.


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## Knotty Fly (Jun 29, 2012)

Try running it with some weight on the bow (a big Buddy or two) to see if it changes anything. We had to reposition the fuel tank and batteries on my Dads old Alumacraft to get it to go away.


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## pmgoffjr (Jul 30, 2009)

Properly adjusted step n trims, along with a good 4 blade prop will help a lot. Just remember that hull wasn't designed to do anything but run flat, so don't try to force it into something it's not happy with.


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## MackerelMan (Aug 16, 2005)

*Motor Height?*

Are you sure the motor isn't mounted to low? Running at plane you should have the cavitation plate riding at or just above the water line. Have someone drive the boat and you go back there and look. Had the same problem with an 18' aluminum Express. Ended up raising the motor by one hole on the transom and problem was solved.


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## texcajun (Feb 22, 2009)

I have almost the same set up as Kelly Joe 'cept mine is a side console. I have done everything I can to this thing, 4 blade prop, Manta Ray copmpression plate, and hydraulic jackplate. I can tame the porpoising with trim but these hulls are what they are. If you try to trim the nose too high, it will porpoise. Like Pat said, they want to run flat. Running flat is what you want your boat to do anyway, and yes you will loose a little top end to make that happen.

And by the way, I had the simple aluminum plate (Whale Tail) on mine and it was inadequate. The full length compression plate is the only way to go. I wasn't lookng for speed, I am trying to get this thing to run as shallow as possible. On plane the only thing hanging below the boat is 3" of skeg.


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## 4xsthefun (Jul 16, 2010)

I ended up going with the 4 blade prop and adjusting step in tabs plus moveing some weight to the front and it helped a lot. I lost some top end speed but it still runs 40 mph which is good enough. The 3 blade would push it mid forties. First tunnel hull for me and I was not sure what to expect. Now the issue is resolved I like it. Thanks for the replies.


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## Txredfish (Oct 27, 2010)

I have a 2006 Alumascape 18' with the tunnel hull with the step sponsons. I am running a 70 HP Yamaha and 4 blade prop. It has manual jack plate which raises the prop in line with the tunnel. No running problems at all with porpoise. It takes straight off without much front hull raising. Runs fast enough for me and very shallow. It is rated for 115. If I had a 115, it would probably be scary fast. I think the 4 blade prop was the key. It was set up at Chris Marine when I purchased the boat. The only problem that I have is that it runs so shallow that sometimes it get me into trouble and I run into a reef and have to push off.


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## CoastalOutfitters (Aug 20, 2004)

you have 2 cheap choices

1 move some weight forward..........coolers , batteries, etc
2 install some transom wedges to give you more neg trim to tuck the motor


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## KEMPOC (Aug 24, 2010)

You will always hate that boat. The only solution is to sell it to me right now!

Seriously, I am in the market if you decide to sell.


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## 4xsthefun (Jul 16, 2010)

*2072 ff*

Hey thanks for the offer but I think we will keep it for a little while. Wanted the tunnel for running around the marshes in upper trinity and river. May venture out in mid bay or lake livingston on really good days. First time owning a tunnel and they do have a different ride and handling. With the porpoising issue gone we can relaxe and enjoy. I am pretty anal about stuff and if it does not work right it drives me crazy( short trip ). Thanks for the replies, 2coolers are usually great for helping out. Jack plate and trolling motor in the future, one step at time.


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## texcajun (Feb 22, 2009)

That boat, my friend, is waaaaay to pretty! Sweet ride! That thing would really respond to a hydraulic jackplate.


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