What is this on the bottom of thr transom? What happens if I cut it off??

[MrMikeTN]

I have a 1989 Riveria Pontoon, FUN DECK, its registered as a 29foot, but the full deck is almost 29foot the toons are more like 32foot.
On the bottom of the transom is a weird shaped hollow angled wedge pocket.
This aluminum pocket is causing a valley or void of water where I need the water (on the prop) when Im about 4000 RPMs or trying to go above 4k.
It causes the prop to ALMOST cavitate or start to "SUCK AIR"
The motor is a 1986 merc 90hp Inline 6, it came off of a 16 1/2 ft fiberglass boat it has a 13" stainless quicksilver 19PITCH prop.
I know I need to change the prop for this boat, Im going to try out a 4 blade 17pitch and a 4 blade 15Pitch. which ever one gets my RPM's up to 5000+ and does what I need it to do will be the one I fianlly buy.

MY QUESTION IS WHAT IS THE WEIRD EXTRA MINI TRANSOM BELOW the NORMAL TRANSOM???

Ill try to attach a few pictures.

Im either going to have to buy a Jack plate that will set the motor back 4 inches and let me come DOWN 3-4 inches
OR
Can I cut the weird whatever it is attachment that is causing the valley or void of water at higher speeds and just have the bottom of the transom FLAT?? it looks as if cutting it off flush would stop the valley/void of water problem.

Ive stopped and looked at about 6 different tansoms on pontoons by other manufacturers and none of them have this "THING".

DO I need this "THING"???? Is the time / space fabric going to come undone and Ill cause a black hole in the universe if I cut it off?? LOL!!

Or should I buy a Reverse (dropping) Jack plate and remount the motor back 4 inches and lower it about 3 inches? AND YES I can TIG WELD IT BACK ON , But Id rather know what it is Im cutting off and what it is for BEFORE i cut it off..

 

[Blujay96]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

I have a 1989 sun cruiser and it does not have one. I wonder if someone was trying to tweak in the water flow for a different motor. I would say cut it off.

 

[crb478]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

I have never seen one like that before, but I suspect that it is there to try to help smooth out the water coming off of the pontoons before it hits the prop. I think that I would leave it on until I tried one of the four bladed props and see how it performs with them. If it is still a problem then cut it off. I can not imagine that it is any help when trying to back.

 

[5150abf]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

Take it off and see what it does, if it is worse you can always have it welded it back on.

Never seen one and it does look like someone was trying to change the water flow but if it doesn't work whack it off.

 

[Fleetwin]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

It looks to me like someone tried to achieve additional negative trim by notching the mount. They added that piece to keep the strength.

I think you could remove it and just reinforce the area with flat plate. Bolt the plate on with SS fasteners.

17" pitch prop. is way too much. You should be in the area of 11"-13" pitch. That engine will NOT tolerate "lugging". You need that engine to be able to turn in the upper range of its RPM band at Wide Open Throttle.

 

[BLC]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

The motor pod on my boat had something similar welded to the bottom of it. It was just a peice of angle welded virticle so that the pointed end of the V was facing forward. I had no idea what it was supposed to do so I removed it and it made no difference. I agree with the above statement on the prop/rpm info.

 

[MrMikeTN]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

JUST FOR FYI:
I cut the weird attachment off the underside of the transom, then used a flapdisk on a 5" right angle grinder to grind and smooth out where the welds were, then took a really fine grit sand paper on a Dual Action orbitial wet sander and polished the whole transom.
Finally I used the grinder and a few cloth cutting/polishing wheels and some jewelers rouge and buff polished the transom to a mirror finish.
IT FIXED MY PROBLEM !!
I no longer have issues with the prop almost sucking air and the cavatation plate stays well under water when the motor is tilted up to level.
Also found a prop dealer who sold me a Stainless SOLAS 4 blade prop in 13pitch WITH the understanding if it dosent get my Rpm's where they belong they will exchange it untill we get it right!!
The Rpm's are now at 4600 @ WOT. So ill exchange it for the pitch they suggest next.. I CANT SAY enough GOOD THINGS about this PROP dealer. They were extremely nice and gave many suggestions, plus a walk thru of excatly how to PROPERLY prepare the shaft and PROP before installing it. The Prop Dealer I bought it from does not do ANYTHING but PROPS, they build their own, modify, fix, service and even sell a few other manufacturers props.(They dont sell many "other" manufacturers props, just a few that they feel are excellent)
If your going to buy a prop and YOU KNOW FOR SURE what prop size and pitch you need then by all means buy it as cheap as you can.
BUT if your not sure then I STRONGLY sugget you find a REAL PROP PROFESSIONAL SHOP.
The shop I found prices are actually cheaper than 99.9% of the internet prop sellers I researched for 2 weeks!!
Now that my tansom is mirror Stainless looking I want to buff polish my toons to match, BUT that will be a large job!! Best tackled with a few buddies, some BBQ and a case of beer..

 

[TurboM700]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

My 89 Bass tracker had one on it before I cut the entire back end off to install an I/O.

The only thing I could see is to help keep weed from getting wrapped around the drive. That little V might kick them out one side or another.

Here is a CL add I seen the other day that had one also.

Pontoon engine motor mounting bracket

 

[Fleetwin]

Re: What is this on the bottom of thr transom? What happens if I cut it off??

Looks to me like a piece to strengthen the transom and acheive more negative trim as pointed out above.

By the way, you are thinking backwards on your prop selection. A higher pitch number will REDUCE your RPM, not increase.