Advice on rigging a 1652 G3 with Jet

[boondockinak]

I have a buddy who has a Dewey's 1852 g3 package with a 50horse yami prop. Obviously a non-tunnel hull as it came rigged for a prop. Recently he bought his own jet package and installed it, along with a CMC power lift. All said and done, due to the thickness of the power lift (5"+/-), the front of his intake foot is sitting somewhere between 10"-12" away from the back of the boat, and he's getting some bad cavitation. He's getting a top speed of about 23mph, and the thing takes forever to get out of the water after take off (probably 8-10 boat lengths) with just he and I in it, even with me moving all of the way to the bow. Also for what it's worth, running a straight edge off the bottom of the boat, off the back of the boat, it looks like the front of his intake foot is sitting about 1/2" below the bottom of the boat. In contrast, I set mine about .25" below the bottom of my little 14' jon boat, 40/30 jet, and it seems to do really well with no noticeable cavitation.

With my limited experience outfitting OB jets, I noticed a couple of things. His g3 has a chine running right down the middle of the boat, which I'm guessing doesn't help to bleed off air from the water by the time it hits the back. Also, my immediate observation is that the 10"-12" of gap from the back of his boat to the jet intake (depending on the trim) gives way to a lot of aerated turbulent water. I'm guessing this is why I see guys running plastic/aluminum horizontally from the back of the boat to the jet intake. Is there a right way/wrong way of doing this? how do you work around the center chine on the bottom of the boat, to feet clean water to the jet? With that much gap, how does a guy go about supporting this piece of material?

Any advice would be outstanding.

-Rob

 

[gpaul99]

Is the lift all the way down when you're trying to take off? What about the trim of the motor, is it trimmed all the way down too??

Usually jets cavitate when the foot isn't at the right angle or is too far out of the water.

You'll want the foot deep down in the water for take off but once you get on step, you adjust the lift up for efficiency (less drag). I would look at the trim of the motor and put the lift lower for take-off. The chine probably isn't helping matters, and ideally you would want a jet tunnel installed on the boat... The tunnel would still work fine with a prop, I believe.

If you post some pics of the setup, im sure we'll be able to better give advice.

 

[fishhook57]

I have seen guys remove the chine for at least 24 inches, and smooth it out, that is for non tunnels though. And then run a flush welded plate back about 4-5 inches and 18 inches wide at the transom angling to about 12 at the pump. Then they take the plastic and run that till it hits the pump, but they recess the lip of the plastic where it rivets on to the plate. That way everything is perfectly flush the whole length of the setup, had a friend a few years ago do this, went from 25 mph to almost 28 according to the gps. That was on a light 1860 with a 60/40. Also got rid of most of the spray too, which was nice. I have always been told not to have more distance from the foot to the transom than what the foots length itself is, seems like a decent rule of thumb. 12 inches is too much.

 

[Akgramps]

Get rid of the strake and the lift, if he is not going to run a prop mount the motor right to the transom. The lift set back is a negative. Then bolt on a piece of aluminum angle to the transom and attach a piece of UHMW to that as a horizontal extension of the bottom of the boat. 1/4" thickness should work nicely 12-14' wide and just long enough for the jet foot to tuck under with the leading edge of the foot 1/4" above the bottom of the boat. Start with just the top two holes for attaching the motor as they are typically slotted and you can make some minor adjustments to height until you get it dialed in....Good luck....

 

[flatbottom]

i have the same boat with a center console 60/40 yam
you want to just use half the lift so the motor mounts high. then its only a few inches behind the back of the boat.
then you want a cavitation plate attached to the transom that covers the top of the motors foot so you get clean water to it.
set the foot so the very back is just below the level of the transom.
then it will plane fairly quickly unless you have tiller steering and no floor so its lighter. then it gets up much faster.
in any case with more tha one person you must have them up front. it is a small boat with not alot of displacement so it makes a compromise boat.
mine does 24 mph and i suspect if i cut out two feet of the center strip i would pick up a few mph.
after on plane you tilt the motor back until just before it starts to cavitate and the bow is bouncing. that is your best speed.
it isnt a three fat person boat.
the newer ones are putting the center console more forward to get the weight forward. you can also move the battery up front with some work help

 

[alaskaowned]

I ran a similar setup. The advise you have gotten so far is good... might want to think about getting rig of the chine like fishhook suggested. More HP would also help! I kept my motor trimmed to about the angle of the transom and just used the power lift to raise it up after I was moving. You can lift the motor higher than you normally would because the motor is set back on the lift. To high and steering will become an issue.. fins help with that. I rigged a piece of UHMW that extended out to the jet.. not for performance reasons, just to cut down on the spray from having the motor set so far back.

 

[boondockinak]

Thanks for the replies. I'll pass this along. He may want to deal with the chine issue, and he plans to do something similar for the cavitation behind the boat, using some aluminum and plastic. Regarding just beefing up/raising up the transom and getting rid of the motor jack, this motor is a long shaft, and he uses the prop frequently, hence the need to raise/lower the motor often.

Thanks again.

-Rob

 

[boondockinak]

Also, thanks to the gentleman who pointed out for me that the thread name and the first line of post #1 is a contradiction. The boat is a 1652, 16' long.

-Rob

 

[keh]

Outboard jets also makes a set of intake fins for the side of the foot that are designed to force more water into the foot. For that pump, an AJ i believe, the part number for the intake fin set is 1185. A bit under $70 for the kit.

 

[lineburns]

A bit late to the party but..... I've been running a 1652 G3 w/ a long shaft 50/35hp Tohatsu on a home built transom lift for several seasons and have experienced a few issues but have ironed them out w/ my current configuration. I do switch to a prop when I need the added power and I intend to stay out of the shallows. I use a 6"x 12" piece of UHMW or HDPE (can never remember which is which) attached to some Al L metal attached to some square Al tubing. There is about a 1 inch overlap, plastic over boot foot and the leading edge of the boot foot sits even w/ the bottom of the hull (reduces cavitation and splash back). I have run it higher but I did have some issues w/ cavitation in chop (small rapids).... trade-offs. With the flotation pods, on step I can run short distances in about 3-4" w/o contacting the bottom. Sits about the same depth empty and about 8" loaded. Two people, gear and fuel I can get on step in 4-5 boat lengths, but need 18-24" H2O to do that w/o worry. I think I've posted several images to my public album but I am not too sure if I was successful.

 

[boondockinak]

I've never seen a jet foot mounted so high on a non-tunnel boat, also have never seen the plastic sheet mounted so high. Everything I've read says that the front of the intake foot needs to be at the bottom of the boat or lower, and that the sheet of plastic needs to be mounted smoothly flush with the bottom of the boat, leading to the intake foot. I don't have a lot of experience with this yet, but from what I've been advised and read, I'm amazed that you aren't getting more cavitation than you are. Most guys running them like I described talk about getting on step in a couple of boat lengths or less, I wonder if a more flush mounting position would give you smoother power, and feed cleaner water to your intake? My other buddy who mounted a new merc 60/40 on his jon boat experienced cavitation when he had the front edge of his intake foot even .25" above the bottom of the boat. Who knows though, difference boats do different things I suppose.

Sounds like this configuration is working well for you. :topjob:

Thanks for the response.

-Rob

 

[JoeMeek]

I have the exact same 1652 G3 with the exact same setup, and have struggled with the exact same issues. I moved max weight forward, added a splash plate, trimmed the motor as high as possible, added the three blade SS Impeller, all worthwhile refinements, but frankly, at the margin. Also, the boat had a 3 ft long, 2 in strake added to the center keel/chine before I bought it [which I will probably remove], but it does not seem to add to cavitation, so I doubt that removing the center chine would make much difference on this boat. The reality is that the boat is somewhat underpowered with the jet (but Kenai legal!], and really skoots with the prop. The heavy motor and lift hanging far off the 15 degree transom tends to unbalance this small boat. You can run trim all of the way in, but it is inefficient and only partially solves the problem. So I added 12x12 Bennett hydraulic trim tabs. Problem solved. With just me in the boat, tabs down, instant hole shot and I can run bow down at 16mph, 4800 rpm. Tabs up, slightly trimmed, calm water, perfect plane at 26.5 mph, 5500rpm. I try to run the trim with the motor nearly vertical, slightly in [about 13.25 inches from the front of the foot to the transom, 5 bars on the trim indicator]. The boat is a compromise, but works for me.