Here is a pic at about 75 or 80 last year with 750 hp

 

I am running the Imco 2" shorties on my Dominator and they gave me a solid 5mph. But they also gave me less bow lift which I needed anyways because when she was into the 90's the boat had too much bow lift and felt too loose. Now it runs faster and flatter across the water and is much easier to control.

 

Like DS said, going to a shorty will take away bow lift. Have you talked to throttle up Propellors??? Also, I would say you have the wrong gear ratio because of the size of your prop, I have always been taught if you have to go over a 30p prop, you have the wrong ratio and are not running efficiantly. Also, I am sure you are running faster then that hull was ever designed for, so you may have a tough time dialing her in.

Good luck

What prop are you running now???

 

Like DS said, going to a shorty will take away bow lift. Have you talked to throttle up Propellors??? Also, I would say you have the wrong gear ratio because of the size of your prop, I have always been taught if you have to go over a 30p prop, you have the wrong ratio and are not running efficiantly. Also, I am sure you are running faster then that hull was ever designed for, so you may have a tough time dialing her in.

Good luck

What prop are you running now???

Then why do they make 30 pitch props? I think you been told a wise tail. There are a ton of fast boats out there with larger than 30 pitch props.

So what speed was the boat designed for? Maybe faster than Baja ever intended for the boat to do, but how was it they designed the hull to go a certain speed?

 

Then why do they make 30 pitch props? I think you been told a wise tail. There are a ton of fast boats out there with larger than 30 pitch props.

So what speed was the boat designed for? Maybe faster than Baja ever intended for the boat to do, but how was it they designed the hull to go a certain speed?

Call TU, they can explain efficiency of larger props to you, you will never believe me.

I am not an enginner at Baja, so I can't tell you what speed it was designed for , BUT, every boat has a maximum theoretical speed when the hull is desined.... Again, call TU or any boat manufacturer... My last personal example...I had a small 16 foot Checkmate with some exstensive work to the power and I had it running in the low to mid 70's. After many conversatios with Checkmate about this, one of their comments was be very careful, that hull was NEVER designed to run above 60. See, there is a thing called hydrodynamics and aerodynamics that goes into the design of a hull and deck and when you put the 2 together, you come up with a theoreticcal speed for what the boat will run. This is why some boats have built on hooks or rockers to help control boats at speeds and when a said speed is exceeded, you can away from those charicteristics and cause handleing problems....
See, when I use to build race boats, we used to design them to run up to around 240 mph. Someone asked what will happen if the boat went over 240...simply, kill the driver. These boats became planes over 170, so we had to have canards to keep a boat ont he water, that is what you call designing for speed...

Got it, but i am sure you won't believe me, so do your research...

 

Like DS said, going to a shorty will take away bow lift. Have you talked to throttle up Propellors??? Also, I would say you have the wrong gear ratio because of the size of your prop, I have always been taught if you have to go over a 30p prop, you have the wrong ratio and are not running efficiantly. Also, I am sure you are running faster then that hull was ever designed for, so you may have a tough time dialing her in.

Good luck

What prop are you running now???

I'm turning a 32pitch labbed at 5800 rpm's. The general consensus on gear ratios I have always heard is when you need taller than a 34 pitch its time to re-gear. As far as what the boat's hull was designed for when i have weight in the back seat and the waters not super rough, it is rock solid and pulls pretty straight.Before the c/g moved from the lighter engine parts the boat never transom lifted either,even at the same speeds(it does it at 60 even if you lean on it with out enough rear weight) I do have imco twin ram full hyd and 20" long trim tabs,boat was dangerous even at 75mph when it had stock steering,Smitty

 

Smitty,,,

so what prop are you running now??? I assume Bravo... Who labbed it?

 

Smitty,,,

so what prop are you running now???

32 pitch labbed merc 4 blade at 5800 rpm's

 

32 pitch labbed merc 4 blade at 5800 rpm's

Bravo????

who labbed it?

 

Call TU, they can explain efficiency of larger props to you, you will never believe me.

I am not an enginner at Baja, so I can't tell you what speed it was designed for , BUT, every boat has a maximum theoretical speed when the hull is desined.... Again, call TU or any boat manufacturer... My last personal example...I had a small 16 foot Checkmate with some exstensive work to the power and I had it running in the low to mid 70's. After many conversatios with Checkmate about this, one of their comments was be very careful, that hull was NEVER designed to run above 60. See, there is a thing called hydrodynamics and aerodynamics that goes into the design of a hull and deck and when you put the 2 together, you come up with a theoreticcal speed for what the boat will run. This is why some boats have built on hooks or rockers to help control boats at speeds and when a said speed is exceeded, you can away from those charicteristics and cause handleing problems....
See, when I use to build race boats, we used to design them to run up to around 240 mph. Someone asked what will happen if the boat went over 240...simply, kill the driver. These boats became planes over 170, so we had to have canards to keep a boat ont he water, that is what you call designing for speed...

Got it, but i am sure you won't believe me, so do your research...

Each year as the boat gains speed from my engine mods I drive it real cautious with a chase boat until i see if its going to do something strange, The boat handles just as good at 91.7 as it did at 75 or 80 mph,obviously if your not careful and slam a huge roller it may flip but ANY v could do that when "riding on the pad". It chinewalked with stock cable steering,the full hyd got rid of that,Smitty

 

You do not have enough boat in the water to cause boaw steer, at least in your pics, and I certainly would not want to carry it any higher at the speeds you are running.

 

Bravo????

who labbed it?

Don't know who labbed it,its a long story involving houston prop but the short version is I used to run a 30 pitch bravo labbed by merc,boat runs 88 mph with that one touching rev limiter at 6000 rpm's. I ordered a 32 labbed from houston prop last fall to try this year but darin sent it un-labbed and told me to run it THEN send it back to him. I sorted bugs out of motor first 1/2 of this season,called him and he was ten weeks behind so I would just be getting it now. Meanwhile I saw a guy selling a 27 ft fountain w/blower in Il on e-bay including a 28 pitch labbed prop. Looking thru his past auctions I seen he bought a pair of labbed 32's (lh/rh),I e-mailed him and asked if he would sell the rh,he said sure,his boat couldn't come close to pulling it and boat was for sale anyways. I bought the prop for real fair price and it gave me almost 4 mph over the 30 pitch so I think prop is pretty good. If houston prop doesn't go under they still owe me a lab job on my stock 32 pitch,I may ask for more cup to get motor down further as it peaked at 944hp on dyno at 5600 rpm's but now I'm going to wait to see what I do for lower unit for next year. If my nose-coned drive gives me 4-5 mph over my regular nosed spare drive then I'm thinking a imco might give me even more BUT I hate to spend the bucks if boat is going to lose bow lift that it needs to get last 3-5 mph out of it,Smitty

 

You do not have enough boat in the water to cause boaw steer, at least in your pics, and I certainly would not want to carry it any higher at the speeds you are running.

You are correct,that occured when trying to run boat wot with 1/3 tk of gas,no passengers,no cooler. With 3/4 tk of gas or a 250 lb passenger in back seat it isn't a problem,Smitty

 

Smitty, I know you have/are working with Houston Prop,,,but my suggestios is to call Julie at Throttle Up propellers. They are VERY reputable and stand behind everything they do and will never take 10 weeks to do a prop. Ask for Julie, she is the BEST!!!

Good luck and congrats on the speeds you are running, I am sure there are not many 272's out there doing what you are doing!! :winker:

 

If you want more bow lift get rid of the hook.
And at those speeds you need a nosecone.

 

This is something new it started doing this year after putting aluminum heads and lighter exhaust manifolds on it (the c/g obviously shifted fwd).

Sounds like losing the pounds on the engine is causing the stern to ride higher and in turn giving less bow lift. I'm sure you could have your prop worked to suck the stern down and give you more bow lift.

With that said, a shortie will reduce leverage and bow lift. But, with some prop work they might work.

 

Smitty, I know you have/are working with Houston Prop,,,but my suggestios is to call Julie at Throttle Up propellers. They are VERY reputable and stand behind everything they do and will never take 10 weeks to do a prop. Ask for Julie, she is the BEST!!!

Good luck and congrats on the speeds you are running, I am sure there are not many 272's out there doing what you are doing!! :winker:

I'm not sure what I'm going to do about the prop,I paid houston prop for a labbed prop and ended up with a standard prop but they (Darin) says he will lab it any way I want,I heard on OSO that he is out of business,I hate to send him back the prop and end up with nothing but I hate to write off the 350$ difference either. Thanks for the congrats,when I first started modifying My boat I thought I'd be happy to get it to run 75 instead of 62,its easy to get carried away,Smitty

 

If you want more bow lift get rid of the hook.
And at those speeds you need a nosecone.

My main drive does have a hydromotive nose cone,I spent some time blending it in good and sharpening the leading edge on it last winter.When I broke it before hardy party I threw my spare on (it has the std xr new style dual water pick-up without a nose cone),boat would only run 87 mph, proof that they actually do something at these speeds,Smitty
here is a pic of what the lower gears looked like when they started to disentegrate.

 

The other thing to consider is if the lower unit is to deep (ie to low an x dimension for your speed).
The lower unit could in fact be imparting positive lift at the transom and preventing bow lift. You do not want a rocker, all you will have is porpising!
In fact going -1",-2" or -3", could help the running attitude, unfortunately unless you know someone with the 'same' setup you have to find the answers.
One plan could be to go -3" (max 14" diameter prop) and come back with spacers if required.
One question are you 'overtrimming' to achieve your speed, ie propsaft not parallel with water surface?
Steve

 

You do not have enough boat in the water to cause boaw steer, at least in your pics, and I certainly would not want to carry it any higher at the speeds you are running.

No doubt, that's whatcha call flying the boat!

 

Have been through this a couple times. Lightning the rear often requires a drive spacer to get the prop centerline back to were it was.

 

This is something new it started doing this year after putting aluminum heads and lighter exhaust manifolds on it (the c/g obviously shifted fwd).

The question is are you trying to get back to how it used to handle? Or are you still looking for more speed? I think getting back to where it used to be before lightening the engine could be obtained by prop work and/or as turbo said even a spacer to get the prop back where it used to run in the water.

Now, if you're looking for more speed that's a whole other can of worms to open!

 

SOUNDS LIKE YOU HAVE A FEW ISSUES REMEMBER DO NOT TRY ALL OF THESE THINGS AT ONCE. IT SOUNDS LIKE YOU NEED BOW LIFT HOWEVER YOU HAVE A HOOK IN THE BOAT THAT IS WORKING AGAINST YOU. THE BOAT IS STERN LIFTING NATURALLY FROM THE HIGHER HP MOTOR AND RUNNING THE BIGGER PROP. THIS IS WHY YOU MAY HAVE HEARD ABOUT N0T RUNNING OVER A CERTAIN PITCH. EVERY BOAT IS SET UP FROM THE FACTORY TO RUN A CERTAIN SPEED SUCH AS YOUR BOAT WAS ABOUT 70-75MPH. YOUR BEST BET IF YOU WANT TO TRY TO IMPROVE YOUR BAJA WOULD BE TO REMOVE THE HOOK AND THEN MESS WITH DRIVE HEIGHTS AND PROPS. MY EXPERIENCE WITH STOCK BAJAS IS THEY LIKE TO LAUNCH BOW UP FOR SURE. AN IMCO LOWER WOULD NOT BE THE RIGHT CHOICE FOR THAT BOAT BECAUSE IT SOUNDS AS IF YOU NEED BOW LIFT AND WHEN YOU START TO TRIM THAT LOWER WITH THE NOSECONE PAST LEVEL YOU WILL SEE YOUR BOAT SLOW DOWN FOR SURE. THAT NOSE CONE WILL ACT AS AN ANCHOR DRAGGING IN THE WATER. ALSO MOVING THE DRIVE UP FOR MORE BOW-LIFT WOULD BE THE WRONG MOVE. FOR SURE YOU DO NOT WANT AN IMCO ON WITHOUT EXTERNAL STEERING. YOU WOULD MORE LIKELY NEED A 1"SPACER DOWN TO GET MORE BOW LIFT. REMEMBER THOUGH THAT HOOK WILL BE WORKING AGAINST YOU. IF YOU DO THIS SHE WILL PROBABLY START PORPOSING IF SHE IS NOT ALREADY. TAKING DIAMETER OUT OF THE PROP WILL REDUCE BOW LIFT ALSO IF YOU HAVE DONE THAT. THERE IS SO MANY ASPECTS TO THIS THAT I COULD GO ON FOR DAYS. 1 CHANGE COULD EFFECT HOW THE BOAT HANDLES AT A DIFFERENT SPEED AND NOT ALWAYS FOR THE BETTER. BELIEVE IT OR NOT A BOAT RACE IS A LOT OF THE TIMES WON RIGHT AT THE DOCK. WHO EVER WENT OUT WITH THE RIGHT SET UP FOR THE DAY.

 

So as I read this, more than likely a boat like mine that runs full trim at WOT would more than likely not benefit from nose cones, maybe even slow it down due to the orientation of the nose cones pointing downward creating more of a drag with the top surface of the nose cone? Theoretically makes sense to me.

 

So as I read this, more than likely a boat like mine that runs full trim at WOT would more than likely not benefit from nose cones, maybe even slow it down due to the orientation of the nose cones pointing downward creating more of a drag with the top surface of the nose cone? Theoretically makes sense to me.

Tom,I don't know if I would agree with that deduction. I think the nose cone helped me but my problem was that I couldn't get enough water to keep the engine's cool long enough to keep it hammered with the side pickup's on the lowers. That is the main reason I sprung for the shorties(for the LWP to keep the water flow.)
Your only talking a couple hundred bucks for nose cones so if you get nothing the sting isn't as bad.
Or you could keep your eye's open for a pair of used shorties and there isn't a doubt that you will get an increase in speed.