# Transom adjustments for jet



## jtf (Aug 5, 2017)

New to jets but the rivers I fish need it. Have talked to two dealers that build a lot of jets. One swears by jack plate and the other warns against it. I found a good used boat that will need re-powering. 

I think it is a 20" transom, does it use a 20" shaft jet. And second, can a transom be raised without a jack plate? It is not a tunnel hull, a 1648 Weldbilt vee.


----------



## Vol423 (Aug 7, 2017)

I have never seen a jet outboard work well with a jackplate of any thickness. The only value of a jackplate for a jet is to raise the motor sufficiently to align the intake with the top of the tunnel or bottom of the boat. If the jackplate moves the intake very far away from the "clean", bubble-free water the motor will cavitate. It is cheaper to build up the transom to the correct height than to buy a jackplate anyway.


----------



## dhoganjr (Aug 8, 2017)

It would be best to have the transom built up. 

Jackplates don't usually work very well with jets. Too much setback, causes excess spray and pushes motor weight farther back. The transom will sit deeper in the water and the bow will ride higher.

If you are going to use a riser, Outboard Jets makes one for the jets.
https://outboardjets.com/outboard-jets-product-catalog/transom-bracket/


----------



## rotus623 (Aug 9, 2017)

If you can find a 15" shaft motor you will not have to build the transom up. Said differently, a 15" shaft motor with jet foot will often work on a 20" transom without building up.

I have seen 60/40 down to 25/20 jets set this way.


----------



## jtf (Aug 12, 2017)

Talked with shop at Tohatsu USA, they fixed me up, got the Weldbilt with 20". Factory says to use the riser mounts instead of a jack plate short shaft and raise 2". 

I have another question, need a welding fabrication shop in east TN to do some minor mods of the 1648 hull. There is one in either Kingsport or Elizabethton, can't find their name. 

Need some storage added and a few other alterations. Would use the same company to rig a new jet outboard if possible.

Thanks for any leads.


----------



## jtf (Nov 22, 2017)

Pulling the boat over to east TN next week for final adjustments at the shop. A few observation and questions. This is a 16/48 Weldbilt with 20" transom 50/35 Tohatsu. Very happy with the clean open floor plan, extra storage for batteries and separated vented deck with 12 gal fuel (two 6gal). 
The fabricator instructed the trolling motor/batteries/tanks/floor be installed to finish tweaking the jet set up. 

I'm trying to put together some ideas/questions to discuss with the shop. 

Here's what's up... 1)Had to move motor up to last mounting holes. I think it needs 2-3 " more transom because the spray gets into hull. Would provide strength with all the motor bracket supported. 

2) Set at best trim, get a bit of cavitation and porpoising. When trimmed down, gets a 6" plume of spray into boat off transom. Trimmed up, less spray but more porpoising and less fast to plane. 

Questions...could it be that the motor need shims to change pitch, or, perhaps a splash guard? Still think it needs a taller transom.


----------



## mphelle (Nov 22, 2017)

Your shop should have at least installed a temporary splash plate to allow you to check out the rig without taking a cold shower. Don't bother thinking about raising the transom until they install the TM and batteries on the bow, a 50/35 will be very sensitive to any weight added and you may end up dropping the motor down. I've been following all of your posts regarding your build, after you receive advice to your questions you should respond with some feedback before moving on to the next problem. It could help people on this forum with similar rigs.


----------



## jtf (Nov 22, 2017)

Will do, have tm and batteries ready to go. The welder/builder weighs 100lb more than I and said it responded correctly with him at the tiller. I put an extra 50lb under me in testing and got splash. We are close. The boat is very fast at full throttle but don't run it that way all the time cruising so need it to down plane.

I was concerned the motor bracket needed the transom rise, maybe not.

THANKS!

Best to all for a good weekend with special folks!


----------



## Scott F (Nov 22, 2017)

Glad you've already got everything worked out. I had a jack plate on my Towee with a Tohatsu 50/35 and the amount of spray coming over the transom nearly filled the boat the first time out. Power trimming reduced the spray or I wouldn't have made it back to the dock.


----------



## jtf (Nov 22, 2017)

Testing set-up. The tanks are forward/vented with batteries in the tan enclosure behind. TM sits left of tanks forward under that bag. The anchors and line sit between two 6 gal tanks. The tanks didn't vent well and put in an expanded metal hatch. TM is appx 65lbs. The rocks are to sub for the 2nd battery. Used 50lb bags of soil to test. I strongly suggest a large vented hatch for these new EPA designed tanks!

It needs just a bit more tweaking, the guys at local shop are all ready asking for a striper trip. So far in three trips, this is the only boat in the last three miles of tailwater under the dam, haha.


----------



## jtf (Nov 22, 2017)

Need a knee/casting brace on bow that is removable and going to work on right-hand side rod tray. Want to get it fly and spin-cast friendly. Thanks for all the ideas of member projects! 

This winter, plan to run three local rivers while no kayaks are in the way and water is clear. Find Feb/March can be terrific smallmouth fishing, not to many fish, but quality fish.


----------



## mphelle (Nov 22, 2017)

Good looking rig. I would have them tack on a temporary splash plate so you can stay dry while you dial it in. I'm getting too old to balance on one leg and a knee brace while operating the TM, could you use an adjustable buttseat?


----------



## JL8Jeff (Nov 22, 2017)

I don't know if my boat is a fair comparison since I have the tunnel. But when I was testing different mounting heights, I kept going up 1 hole until I got excessive spray and then went back down 1 hole. I had porpoising with it trimmed in all the way and the spray got worse as I trimmed it out (so that's opposite of what you're having). I added the transom wedges to get it trimmed in a little more and that was the sweet spot. I can run full throttle with it trimmed in and get no spray but if I trim the motor up just a little bit, I get spray. But my motor isn't in the water as far because of the tunnel so my spray isn't bad. It seems weird that you get more spray when it's trimmed in farther, unless you have it mounted too high and being trimmed in is causing the water to bounce off the front edge of the jet intake.


----------

