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Cavitation plate 2 inches below transom, worth raising?
- Thread starter EddiePA
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Siguz
Well-known member
Where did you buy it/order it from?EddiePA said:
Charger25
Well-known member
Yall gonna make me buy one before its over lmao
whitetailhntr
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Siguz said:
X2
Went for the first test ride today. With the outboard trimmed in the position that yielded the best MPH without the jack plate (second hole out from full in) and the cavitation plate level with the bottom of the transom, the boat actually lost 1mph and gained a TON of porpoising. Even with the fuel tank placed in front of me as far as the fuel line would allow (didn't have a problem with the tank behind me previously) and the anchor at the bow, the boat was NOT happy. It wanted to porpoise unless I was leaning forward with my hand barely on the tiller. For the hell of it, I went to the third trim hole out and the boat didn't want to plane at all unless I let go of the tiller and leaned way forward. Porpoising was out of control. Also at these settings, the prop wanted to blow out in turns.
It seems the engine being set back that additional 4 inches AND being raised up 2 inches is creating enough leverage that the bow doesn't want to settle. It would probably be ok with a second person in the boat, but I still have a loss of speed, at least with the outboard at this height. I could try raising the outboard an inch via the jack plate, but I think that will worsen the porpoising condition (even more leverage) as well as prop blow out while turning. I tried removing the trim pin to allow the outboard to go full in, but it didn't noticeably help. Lowering it an inch may help, but then I will be adding drag and defeating the purpose of the jack plate.
Also, I noticed quite a bit of water riding up the leg of the outboard. This didn't happen without the jack plate when the cavitation plate was 2 inches below the bottom of the transom.
It seems the engine being set back that additional 4 inches AND being raised up 2 inches is creating enough leverage that the bow doesn't want to settle. It would probably be ok with a second person in the boat, but I still have a loss of speed, at least with the outboard at this height. I could try raising the outboard an inch via the jack plate, but I think that will worsen the porpoising condition (even more leverage) as well as prop blow out while turning. I tried removing the trim pin to allow the outboard to go full in, but it didn't noticeably help. Lowering it an inch may help, but then I will be adding drag and defeating the purpose of the jack plate.
Also, I noticed quite a bit of water riding up the leg of the outboard. This didn't happen without the jack plate when the cavitation plate was 2 inches below the bottom of the transom.
PatinIdaho
Well-known member
Here is what I noticed with my setup.
I raised my cav plate to be level with the bottom of my transom and it just did not work well at all no matter what I did.
So I lowered it 1 inch and things improved ALOT.
What I discovered was there is a rib, keel or what ever you call it running down the center of my boat that I believe was the problem.
My cavitation plate is now level with that and its all working together now just fine. Might try what I ended up doing and see if that helps?
I raised my cav plate to be level with the bottom of my transom and it just did not work well at all no matter what I did.
So I lowered it 1 inch and things improved ALOT.
What I discovered was there is a rib, keel or what ever you call it running down the center of my boat that I believe was the problem.
My cavitation plate is now level with that and its all working together now just fine. Might try what I ended up doing and see if that helps?
Lowering it an inch below the bottom of the transom (like you did), as I see it, is the only way to go as raising the outboard further, I believe, will worsen my current issues. I gotta say, if that doesn't make a dramatic improvement over what I started with without the jack plate, IMHO, it just isn't worth going through the trouble of buying and installing the thing on a boat this size and it's intended purpose (fishing in smaller lakes). I have a feeling I'm still going to have porpoising issues even after I lower it an inch as it being set back 4 inches is just too much leverage on this little (12ft) boat. Perhaps on a longer boat, say at least 14ft, the set back might help. Not convinced it's an attribute on something this small, however.
Boat2fast
Well-known member
Thank you for sharing your experience. All your time/trouble/expense may not be completely wasted if it saves others from bad result.
My experience with similar setups is always to try a 3/4in shim to elevate the engine. If it results in a benefit(usually), then keep it. If it hurts(occasionally) then remove it and there is no loss.
I have a real fast SeaNymph 14R/Johnson 30; the shim hurt. Prop ventilated continually. Without the shim it was fine.
Your 29mph was a great result. It's not often the boats go that well. Yours rode nice and straight too, judging by the video.
The picture is a 1969 Evinrude Sportster 25 on a 10ft SeaNymph. Boat went best with the shim and a 2blade brass prop. 34mph/gps
My experience with similar setups is always to try a 3/4in shim to elevate the engine. If it results in a benefit(usually), then keep it. If it hurts(occasionally) then remove it and there is no loss.
I have a real fast SeaNymph 14R/Johnson 30; the shim hurt. Prop ventilated continually. Without the shim it was fine.
Your 29mph was a great result. It's not often the boats go that well. Yours rode nice and straight too, judging by the video.
The picture is a 1969 Evinrude Sportster 25 on a 10ft SeaNymph. Boat went best with the shim and a 2blade brass prop. 34mph/gps
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onthewater102
Well-known member
Before you write off the transom jack could you please post a pic of the setup in the two pin configurations you tested it once you installed the jack?
I pulled the jack off the boat for now, so I can't post a pic of those trim positions. The boat wasn't safe to run with the jack on and I'm using the boat as often as possible (several times a week). When I get more time to test I may try the jack again with the outboard an inch lower than before.
