Stern lifting prop on 14' Alumacraft V w 30 E-tec?

[CG Rob]

Hi everyone,

I have an '85 Alumacraft T-14XL 20" transom that I am working on. It is a project boat; I plan on adding decks and changing the layout a bit. To kick off the project I repowered the boat with a '16 E-Tec 30 w power trim and electric start. The original '85 30 (which I still have) is a low hour motor and runs flawlessly, but I wanted the convenience of power trim and the better fuel efficiency.

Being that the new motor is roughly 30 lbs heavier, I am having more problems with porpoising than ever. When I am alone in the boat, I must run the engine trimmed all the way in and there is still a good amount of bounce in the bow. Moving the fuel tank and battery forward has done almost nothing to help. When I have my two boys in the bow, it runs much better, however I still have to run with the trim close to being all the way in. Having to keep the engine tucked so far in wont let it reach the revs it should, thus killing top end and fuel economy.

I am going to upgrade to a stainless prop, and was thinking that a 4 blade prop might help lift the stern a bit and help the porpoising issue I'm having. If I were to go this route, should I drop 1" in pitch going from a 3 blade aluminum to a 4 blade stainless? My WOT rpm's are 5980-6000; right at max revs for this motor. That is lightly loaded and trimmed out about a third, but the porpoising causes the boat to be almost uncontrollable. The stock prop is a BRP 10.3x12x3. Do you think since my revs are so high that I should try a 10x12x4? Anyone have a similar setup with the same issues?

Thanks in advance for your input!

-Rob

 

[fl.graderman]

I personally found that just going from aluminum to same pitch stainless is going to increase rpms. I think you can go from aluminum to same pitch 4 blade stainless and probably keep your rpms about where they are now.
THIS IS MY OPINION AND I CANNOT GUARANTEE THIS.
That being said...if it were me, (and I did this), I would buy a 4 blade aluminum and drop it down in pitch by an inch. Aluminum props are much cheaper, and even if the results aren't what you were hoping for, you have a spare prop.
Just out of curiosity, have you considered smart tabs? My little boat is very stern heavy and that's the route I went. Best upgrade I've made!

2015 Tracker Grizzly 1448 MVX
1996 Evinrude 25hp 3 cylinder looper

 

[CG Rob]

Thanks for your response fl.graderman!

I hadn't considered smart tabs- I think I will look into them. Anything that will help keep the bow planted would be a huge improvement.

-Rob

 

[fl.graderman]

They look a little funny back there, but they made a huge difference in time to plane and my tilt setting went from the second pin up to the fourth pin. Besides, I can't see em from where I'm sitting in the boat anyway...ha ha.

2015 Tracker Grizzly 1448 MVX
1996 Evinrude 25hp 3 cylinder looper

 

[turbotodd]

Some of the PT&T motors had bolts in the bracket, that stops the motor from "tucking" all the way, similar to the old manual tilt models that had a quickly removable pin that you can change its position on the water. I usually have to adjust them on the Yamaha motors, so that they'll perform properly. They are tucked too far from factory. Perhaps the ETEC's have them? I have not looked at an ETEC in the last 5 years or so, and even then they was manual tilt.

Also, could be a function of the hull. If it's porpoising badly, chances are that a simple prop change won't give you what you're looking for. At the back of many hulls, where the transom comes down and meets the bottom, there is a weld bead where they meet. It serves 2 purposes. One, it holds the two pieces together and two, it also helps keep the boat from porpoising. Yes there is a very slight speed reduction (I saw 0.3 mph by partially removing my weld). If yours doesn't have a bead, you can use JB weld and accomplish the same thing. Just right at the back of the hull. If that works and you're worried about knocking the JB off, you can have it welded....or...some of the guys around here beat the hull in with a hammer, just forward of that weld, which accomplishes the same thing. I call it a forced hook. I usually lay a straight edge along the hull, fore and aft, with the tip of the straightedge protruding past the transom slightly. Then see what the hull is doing. If it's got a rocker in the last 24" (rocker is concave, like dented from the inside out), then it will be more likely to porpoise. A hook, on the other hand, is the opposite (beat in from the bottom up), and sometimes adding a little hook to a hull will fix porpoising.

One would think that a hull is a hull is a hull....but especially with aluminum, even the exact same hull, one is different from the other. Lot of times I'll see one roll off the line perfect. Next one, imperfect. Welding can warp them, as can a lot of other things. Then sometimes when they are welded, they don't build that bead up enough and they porpoise. Or sometimes I see them with the bottom of the boat all beat up, with some rocker toward the stern-which will cause porpoising in a lot of instances. Sometimes they just come that way due to manufacturing processes, and in those cases the only options are welding and hooking. Local guys put a forced hook in, and they do this with great success. I could use a little on mine but I'm scared honestly....hate to bash in the hull that I saved for many years to afford.

 

[CG Rob]

Thanks for the info fellas!

I guess what has me perplexed is the fact that with the old motor, I had very little issue with porpoising. I didn't have power trim, so I ran it on the next to last pin hole in, sometimes even the middle hole. Now the motor is trimmed in as far as it will go, and I still get a fair amount of porpoising. I can't help but think that the extra weight of the new motor has really thrown the balance off. I will certainly check the hull for hook or rocker. I'll let you guys know what I find out!

 

[Pappy]

Or you may want to try a set of inexpensive transom wedges. They go between the transom bracket of the engine and the boat transom. Gives the set-up a bunch more negative trim for pretty cheap. No parasitic drag either.

https://www.ebay.com/itm/like/271936220662?lpid=82&chn=ps&ul_noapp=true

 

[turbotodd]

Or you may want to try a set of inexpensive transom wedges. They go between the transom bracket of the engine and the boat transom. Gives the set-up a bunch more negative trim for pretty cheap. No parasitic drag either.

https://www.ebay.com/itm/like/271936220662?lpid=82&chn=ps&ul_noapp=true

Thank you for sharing! I totally forgot about those, and someone called me recently with a similar issue (porpoising)-and I may mention the wedges to him just in case he wants to go that direction.

 

[woodscavenger]

Not an expert here but I would check the current angle at minimum trim then remount the old moter and check the same. Are you simply dealing with a geometry problem? If the new one can't get to the same angle or less then the transome wedges should be a simple fix.

 

[richg99]

If the wedges don't do it...check out the Smart Tabs that Fl.Graderman suggested. They are super. richg99

 

[CG Rob]

Hey everyone, thanks for the ideas!

Sorry I haven't been posting. I haven't had the boat in the water for the last two weekends due to the crummy weather we have been having here in VA, and my daughters college graduation last weekend.

I did however go out and compare the transom brackets on both motors. They are identical as far a max negative trim angle. That, and the fact that the transom is angled at about 75* leads me to believe I have plenty of negative trim available. So, as far as I can reason, the transom wedges won't help my situation. Looked into the Smart Tabs as well. This may be a good solution, however I am still playing around with engine height and will likely rearrange some weight before I drill more holes in the transom. I also talked to Ken at Propgods. He thinks the PowerTech SRA4 would be a good choice that would help the porpoising issues I'm having. I just need to take the boat out and get some good RPM numbers to determine the pitch I'll need. The boat porpoises so badly now I'm not sure my readings are accurate. I'm thinking about throwing 100 lbs up front to keep the bow down just I can get some decent tach readings. ( If it ever stops raining )

I'll keep ya'll posted.

-Rob

 

[richg99]

Five-gallon paint buckets; filled with water; capped; and tied down securely will weigh about 42 lbs each richg99

 

[beagler1]

They look a little funny back there, but they made a huge difference in time to plane and my tilt setting went from the second pin up to the fourth pin. Besides, I can't see em from where I'm sitting in the boat anyway...ha ha.

2015 Tracker Grizzly 1448 MVX
1996 Evinrude 25hp 3 cylinder looper

I need the same kinda of plate for my ob. I have the same style transom and have me engine too high up.

Info on your transom plate? Please.


Sent from Mossy Oak Swamp Bottom

 

[fl.graderman]

That's a mini manual jackplate made by Bob's Machine Shop. It was right around $200 if I remember correctly. The company is based in tampa, but I got mine from a boat dealer in Orlando.

I should add that they have two sizes depending on the width of you engine bracket and I went this route because #1 I didn't want to spend $700+ for a hydraulic jack and #2 because the cast aluminum mini jacker from th marine didn't look stout enough for my 156 lb motor.

 

[beagler1]

Pm me info on the tampa location where i can get one from the tampa area.!im there alot.


Sent from Mossy Oak Swamp Bottom

 

[fl.graderman]

Pm me info on the tampa location where i can get one from the tampa area.!im there alot.


Sent from Mossy Oak Swamp Bottom

PM sent

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[gunz]

I had this problem on my dad boat with the 25. His transom has quite a bit more "tuck" toward the bottom as mine did. All the way down was not far enough due to the negative angle. I made some wooden shims and fixed it.

I didn't want to install trim tabs due to parasitic drag and knowing ti handled better with the old 18 as far as porposing. Ended up being for not as I removed the 25 and went to a 9.9 4 stroke Honda. he loves it but still trimmed way down due to the transom angle.