What am I missing here? - Installed Bobs Nose Cone & All I Got Was INSANE ChineWalk??

Rig: 16ft 1979 Checkmate Predictor (no back seat, very minimal gear, always run with passenger and black lab)
150hp V6 Merc 78-79 Range I believe
23P Cleaver "Style" 4 Blade Prop (do not believe it is a real purebread cleaver)
Full Manual Adjust JackPlate (4" Setback)
Bobs LWP Nose Cone w/ Fully Molded & Blended Water Piping, Torque Tab, Torque Fin Removed for Delete Plate

Working on: Venting Engine Cover
Foot Throttle
Solid Motor Mounts

Me: Grew up on the river. (Dubuque, Iowa - Mississippi River)
10+ Years Experience Working in the Marine Industry
Current Work in; Mechanical Design / Project Management
(By no means trying to brag, just trying to illustrate my ability to comprehend forthcoming discussion on topic)

Backstory:
I have been running this boat since last season, but just started making some modifications to the setup this season. The boat is very light overall and has always been a fun and consistant performer for me. I would honestly prefer to stick to my stand up jet ski, but my wife likes to get our lab out on the river with us too and that was the reasoning for the boat. What attracted me to this boat in the first place was its general power to weight ratio and its ability to literally surge out of the water with application of the throttle.

Change #1 JackPlate:
Before the installation of the jackplate is had very very minor chinewalking around 58-62mph.
After jackplate install proper height was found there was ZERO chinewalk all the way up to 62mph. Oddly though no additional speed was gained still stuck at 62mph
(GOOD)

Change #2 Bob's LWP Nose Cone:
After a good 30-40 hours of bondo, sanding and painting the lower unit looked absolutely gorgeous. But she turned out to be for looks only...... After the lower unit modifications this boat has been absolutely rediculous to drive it is honestly even hard to call what this thing is doing CHINEWALKING, it is more like hopscotching or breakdancing. The boat will still somewhat surge up out of the hold and rush up to 45ish or so but then it is nothing but jumping from the water side to side sort of like a teeter totter. Top speed is still basically 62mph if I can manage to hold onto it for that long.

I have moved the jackplate all over the place up and down, tried lots of trim, no trim, more weight in the boat, less weight in the boat, weight in different places in the boat. I have tried to drive through the hops, I tried a 3 Blade 23P. Nothing I have done has really seem to make any difference on this thing at all.

WHAT AM I MISSING HERE???

The only thing that I can think of that I have tried yet to get me back to previous smooth predictable handling is spacing the motor out further from the boat the same amount of lenght that was added to the front of the lower unit. Sadly thought this will bring about changing another variable in that the prop will then also be further from the boat...


Recap: Added Jackplate = GOOD, Improved handling, smoother ride (Wierd no speed change but oh well)
Added LWP Nose Cone = SUPER BAD, Virtually uncontrollable handling and again no speed change

HELP! I was looking for a little more speed, but now I just want my old setup back! What I am missing here???

None of this may be what you want to hear, but...
You are not really running in a speed range where an extended nose cone would really benifet you. The lower unit's aspect ratio is now increased and if you are running a bit of positive trim, you have more drag in the water.. The lower unit it acting like a deep dragging rudder..

Its the general acceptance that the Bigfoot lower is mostly effective on boats running faster than 80 mph.

Unless you are partially surfacing the torpedo and running it pretty level to the water, an extended nose is probably a step back....as you are finding.

If cooling is an issue, I've been able to run some pretty high motor heights in the past by simply plugging a couple of the top water feed holes and grinding a little "lead in" channel for the water to direct in. I don't think you are going to run the motor higher on that hull of yours than most guys do on Hydrostreams and similar boats though.

Rev,

Thanks for the reply. Appreciate the info.

I was aware of the 80mph mark before doing the nosecone. My logic behind the nosecone was for the low water pickup, I didn't want to chance running it out of water. Looking back on it, I wish I would have just run the Merc Water Pick Up Scoops, or even just left it alone. I had also hopped to raise the motor a bit and gain a mile per hour or two.

What I am not understanding with my situation is the seemingly random appearance of horrible chinewalk after the nosecone install. I have a very technical mindset and just cannot understand the variable that was changed to produce the erratic handling.

What is also surprising is that post nosecone install, motor height does not seem to affect handling at all compared to pre nosecone runs.

I have run the motor virtually the full length of adjustment in each direction of the jackplate and the chinewalk is virtually unchanged.

With the current jackplate hole setup i am able to run basically at the centerline of the bullet level with the pad of the boat.

Weirdness = motorheight has no effect on speed or handling
Weirdness 2 = nosecone caused irratic handling & chinewalk

My mind is officially boggled.

not trying to insult your skills or anything but are you absolutely sure the nose cone is on perfectly straight?

Edit: do you the solid mounts in?

With some pondering from my pops and his group of "go fast guys" I believe we may have found the root cause of the issue.

The general hypothesis that we have proposed at this time is that the erratic chinewalkyness was brought on by the install of the torque tab on the skeg, removal of the torque fin on lower unit and less than new motor mounts.

So the theory is that where the motor/prop was previously able to take its natural torque and run with it, the torque tab on the lower unit is counter acting it somewhat, but with no help from the motor mounts. Essentially causing a bit of a back and forth wobble on the motor where it was previously just pinned to the one side for the most part.

We are guessing that this is why I am seeing the irratic chinewalk deal earlier in the speed range and is not being changed at all regardless of engine height as the skeg will still need to run in the water regardless.

So it appears to be the perfect storm of: a generally light boat, transom lift prop, less than perfect motor mounts, all coming together to cause some bad handling characteristics.

------ Now the question is do I grind off the torque tab i just installed, go with solid motor mounts or maybe it will take both?? ------

yeah...getting solid mounts in will really help!

Why are you running a Cleaver prop on that hull anyways? Checkmates are not known for being lightweight and I would think that you would need some type of round ear on there to get bow lift not transom lift. Solid mounts are a must to get it to handle right over 50. Do you have single cable steering?

First off the nose cone is not needed at all. Its just an anchor at this point for you. If your steering/engine mounts had any play before you were probably pushing your limits without the cone for stability.

I run a standard gearcase 1 inch below the pad. If your worried about PSI get yourself a 30 dollar water PSI gauge and watch it.

Putting a cone one front adds LEVERAGE to the front of your case for water to push it back and forth if your steering is not perfect.

The front of a standard gearcase roughly starts behind your swivel point for turning. With the major area of drag farther behind the swivel it is more stable. Kinda like fletching at the rear of an arrow.

Now you move your nose out and fwd with the cone and you put the drag farther fwd and it can make it more unstable. If it has a 1/4 inch of play that cone really grabs out front. Running them deep is drag. Once they are up and out of the water they can help...

Conrad

Hate to say this, but it seems like you should be faster anyway. Your boat is similar to the JP OPC boats I ran with back in the 70s-80s. I don't think that the Checkmates were still competitive then--Allisons, Hydrostreams and Actions, but those boats (150 XS motor with built in LWP) ran up into the 80s. It sure seams like, even if the hull isn't quite the same and you may be a little heavier, that you should be in the 70s.

Is it just me or is there some serious irony that the boat is "totally uncontrollable".....and it called a "Predictor" :eek:

I think Conrad explained really well what is happening. It makes a lot of sense. I had not considered the pivot point vs. leading edge factor. Add in the afore mentioned postive trim angle and you really have a floppy rudder.

Take an imaginary look at the front of the torpedo as it is running through the water at speed, with trim angle included. This is your "window area". With an extended nose, this area gets much larger on a quick hurry. I'm sure it's still a linear equation, but the percentage of window area before and after is drastically larger with the cone.

Sorry, I had to borrow some cylinder head porting terminology..but I think you'll get what I'm saying.

I dont believe I have seen any mention of what type of steering your running. Some are sloppyier than others. JMO

Lots of good thoughts and info here. My vision of this issue is starting to clear up.

I loved the "totally uncontrollable".....and it called a "Predictor" :eek: comment, never thought of that, made me laugh!

I do have a single cable on it right now but it is surprising fairly precise.

It seems like we have most of the causal factors figured out, does anyone have any thoughts on solutions?

*Do I toss a stock lower unit back on?
*Definitely going to do something with the motor mounts
*Should I grind off the trim tab if I keep the lower unit on?
*Likely will continue trying different props
*Have meant to get a water pressure gauge in the boat... What PSI limit 15 or 30?

I am still hoping to get more speed out of it if I can. Not really sure why my speed aspect hasn't changed one bit after all of my tinkering; props, jackplate, lower unit, weight, etc.

I am guessing I just still need to get the "right" prop on it.

theres more to it than just the prop...there are three things here that are a must have....first ditch the single cable steering ASAP...get dual cable (preferably opposing entry) or get hydraulic...second get the solid mounts in it (this combined with the steering should drasticly improve handeling) third get a foot throttle so you can keep both hands on the wheel and if something does go wrong the throttle will return to idle on its own...those three things manditory in my opinion!...once ya get the handeling figured out the speed will follow with more set up work and propping.

Hey Johnson PM me I'll try to help you with some setup issues. MDevrow

34 year old whipped out motor mounts and a single cable = flip flop.