'74 Tahiti Berkely pump/Place Diverter trim/proposing issue.

[Nikwho]

Hello all,
I have a question about trimming my hydraulic Place Diverter. If I trim up much at all, the boat starts propoising. It starts porpoising about the time that the pump discharge stream gets about two to three feet out of the water. Boat runs well. I don't need to run around with huge rooster tails, but mostly just curious as to why it won't run with more up trim than it will.

Is this something that a droop might resolve? Berkeley 12-JC pump. Place Diverter. Will swap to a split bowl if need be to get the boat to run better. I'm thinking that if I could get the boat a little further up out of the water, it could improve top speed. Thoughts?

 

[coolchange]

That hull has a big hook in it. Probably. 2-3 feet is right for best speed. A ride plate might help. Taking the hook out will get you a big speed gain but sacrifice handling. I assumed it was a 19 mini?

 

[Nikwho]

Thanks for your response! It's a '1974 Tahiti Super Tiger. 18'. I can get the water stream up 2-3'. If I try to trim it up any further, it immediately purposes pretty severely. I'd say at 2-3', it starts a mild porpoising.

If I'm going to try to take the hook out of the hull, I'm assuming that's via a straight edge, blocking and some fiber strand epoxy filler, followed by paint? If doing work already that invasive, would a pump set back likely be worth the effort?

 

[Nikwho]

I will say, at this point I have a pretty healthy 455 Oldsmobile that the previous owner built up some. I, however, am currently building a 496" BBC with Brodix heads and solid roller cam. Lookin for honest 650-700HP. Some people work will be in order. Would like to establish a game plan that will make all parts compliment each other. I'm going to pull the pump to send to a reputable builder when I pull the engine for that swap.

If straightening the hook, a ride plate and possibly a pump set back are in order, I most certainly would like to do that will it was already blown apart. Mounting the BBC on a rail kit. I have a rotisserie that I could flip the hull with.

 

[lantz]

I think that is normal. You should have a sweet spot though as you trim up: the bow spray will move back, the motor will quiet down as it's not working as hard, and the steering gets a little easier and responsive. Once I get there, any higher on the trim, and i get to bouncing unless i've got a full load of kids or a couple of dads in the bow. Looking back when I get there the water stream is just high enough to mess up the water in the wake...not that a jet has anything close to a clean wake ever....

 

[Nikwho]

So, are some hulls just more prone to it? Probably hulls with more hook, I'd assume?

My immature side would like to be able to play with a big rooster tail, albeit totally unnecessary.

 

[coolchange]

So that is like the south wind hull. First I would check the bottom for true so you know what your working with. Know that it could have a tendency to spin if you take the hook out. That’s why it’s there. That hull is going to hit the wall in the 70s and cost exponentially beyond that. Check with SoCal jet boats. Someone there has done this road.

 

[Nikwho]

That's good to know! I've been loosely on the hunt for a good winger hull for a while. Not looking hard, but keeping eyes out. I may just lean towards leaving this boat as it sits, and saving my 496 for a CP gullwing, when I find one. Almost pulled the trigger on a really good looking grey and lime green one in Louisiana. Dragged my feet and it sold to someone else. Something to be said for keeping this boat functioning, while I build a new boat! Then I can take more time building and rigging it right.

 

[old rigger]

So that is like the south wind hull. First I would check the bottom for true so you know what your working with. Know that it could have a tendency to spin if you take the hook out. That’s why it’s there. That hull is going to hit the wall in the 70s and cost exponentially beyond that. Check with SoCal jet boats. Someone there has done this road.

that's pretty funny.

The hook was not built into the bottom at Tahiti or for that matter at any other shop I worked at. That's a myth. At Tahiti and other production shops, hook was put in the bottom usually from 2 things, the rigger installed the intake improperly or the part was pulled from the mold too soon. Seeing's how the part sat in the mold overnight before being pulled at Tahiti, Hawaiian, and all the other big shops in the 70s then pushed out into the sun until ground instead of sitting for a few weeks or a month, there's your hook.

Sitting on the trailer wrong will also add hook. Roger was obsessed with the trailer bunks from our trailer suppliers and sent more than one back.

 

[coolchange]

Ok

that's pretty funny.

The hook was not built into the bottom at Tahiti or for that matter at any other shop I worked at. That's a myth. At Tahiti and other production shops, hook was put in the bottom usually from 2 things, the rigger installed the intake improperly or the part was pulled from the mold too soon. Seeing's how the part sat in the mold overnight before being pulled at Tahiti, Hawaiian, and all the other big shops in the 70s then pushed out into the sun until ground instead of sitting for a few weeks or a month, there's your hook.

Sitting on the trailer wrong will also add hook. Roger was obsessed with the trailer bunks from our trailer suppliers and sent more than one back.

ok well that’s what I’ve been told. Never saw one without hook. Took the hook out of my Tahiti and put full stringers in it and you could spin it out in a turn. Pump angle or what ever it was.
that’s pretty funny.

 

[Nikwho]

So, what is the preferred way to handle the hook in the hull? What's the preferred way to diagnose if/how significant a hook is? A straight edge?

 

[mash on it]

So, what is the preferred way to handle the hook in the hull? What's the preferred way to diagnose if/how significant a hook is? A straight edge?

I've passed on buying more than one jet böté just from eyeballing the bottom from the rear on the trailer.

The important part is the last 6 feet. A bad hook or rocker is easy to see.

How the intake was set can make a huge difference. I reset the intake on my Saguaro, the front was at least ¼"+ hanging down, and not quite level left to right. (Böté did 52 with a 460 ferd, and right at 60 with an SBC, a win-win). I know the bottom wasn't perfect, but less than an ⅛" hook where I could check. I figured that was good enough for a fishin böté.

Dan'l

 

[old rigger]

I've passed on buying more than one jet böté just from eyeballing the bottom from the rear on the trailer.

The important part is the last 6 feet. A bad hook or rocker is easy to see.

How the intake was set can make a huge difference. I reset the intake on my Saguaro, the front was at least ¼"+ hanging down, and not quite level left to right. (Böté did 52 with a 460 ferd, and right at 60 with an SBC, a win-win). I know the bottom wasn't perfect, but less than an ⅛" hook where I could check. I figured that was good enough for a fishin böté.

Dan'l

most important part of a boat and you’re smart to check it out. It’s the first thing I look at regardless of brand or drive. Our Spectra is an I/O and it’s got some hook in it, not much but enough you can see without a straight edge. Maybe 3/16s, but it’s just a 50 mph cruiser so I didn’t care. All the old Tahiti’s I’ve owned had zero hook but the were outboards and I/Os. The one jet I bought to flip had some hook though and I’m sure it was from the intake.
Our neighbor at the river has a 21’ Roger’s I/O and it’s cockeyed and too far back on the trailer and it has a shit ton of hook, maybe 3/4 of an inch. He doesn’t care, poor thing just sits cooking in the sun while his roll bar boat is in the garage.

 

[old rigger]

Ok

ok well that’s what I’ve been told. Never saw one without hook. Took the hook out of my Tahiti and put full stringers in it and you could spin it out in a turn. Pump angle or what ever it was.
that’s pretty funny.

So did the boat only spin out after you worked on it or before too?

 

[Nikwho]

I'm also curious, what is ideal? A perfectly straight bottom, with zero hook? Sounds dumb, and seems obvious, but I know too little to make assumptions!

 

[mash on it]

I'm also curious, what is ideal? A perfectly straight bottom, with zero hook? Sounds dumb, and seems obvious, but I know too little to make assumptions!

Mine is. '74 Miller SJ, flat deck.
Down side up at the moment.

Dan'l