HELP!!!! chris cat
 

86 chris cat
900sc's (true 900hp)moved 2' forward, SSM IV drives with boxes 4 blades 33 x 17.5 turning in
the boat is running 109mph @ 5000rpm
terrible porpus over 95mph so bad its coming out of the water with any positive trim (have only run the boat 1' chop mixed with some boat wakes).
is it the water conditions, prop direction, do i need more power to drive through it whats the cause and problem?

you need wings!!!!

Just a quess,,,did u try to turn them in??? But don't run them in reverse !!!!!!!! Change the drives !!!!!!! ITS NOT LIKE ON A BRAVO !!

I think it helps with handling ,also,,,how high is your X-dimension (drive hight ) ???

its about an inch or two about the bottom of the boat.
someone else also told me to try to switch the drives (turn the props out) what will that do?

Make the props turn the other way! :evilb:

You need to get a good measurement on the drives, "an inch or two" is like a mile when playing with x dimensions.

A friend has a pair 750's in his and its at 117mph, so with 900's it should be way over that.

Any idea of your slip numbers?

Chris Cat
 

Cody, I think you are getting too much bow lift. The people that can help you are George Linder and T2X in this site. X dimension is crtical on these boats as is prop selection. You have all the power you need, where are you located?

Wannabe

From my experience I think you need MORE bow lift... when I went from stock lowers (bravo's) that were 2'+ lower then the hull to a -2 lower - my porpoise range went from 70-80 zone to 90+ leading me to believe I have lost some ability to carry the bow resulting in a porpoise that take more air & faster speeds to disappear, I turn mine props outward, not sure if this helps? I plan going with a prop that has been worked a bit to help carry the bow high - then I will know for sure

Cody, we need more info. X dimension, prop diameter,engine placement etc. My 85 chris is worst on flat water with extra weight in the front. I believe you need More bow lift. There are 3 linder hulls rigged with Speedys near me, including mine. I would be glad to share info etc. The props turn in on all three, in lifts the nose...the higher the x the more necessary they spin in. Good luck, These boat are have an awesome ride in the rough for their size and they can be very efficient once set up correctly.:drink:

??
 

i will measure the drives
the motors are further forwardi will post a picture.
when the props turn in does it lift the bow or transom?

props are mercury 4 blade 33 X 17.5

There is some useful info in the folowing post, its pretty long but I found it very informative!!!! http://www.offshoreonly.com/forums/g...t-history.html

Cody,,,i know a guy that has 1 inch spacers and u need to defenitly rais the drives up even more ,,,,porpousing is because the drives are to low,with the 2 inch spacers u have.
But ofcorse spinning them in helps a little ,i don't think enuff though.

Scott

Definitely raise the drives. You are getting too much transom lift. You might want to try a little less diameter on the props before you go about raising the drives- should have roughly the same effect and let you know if you are heading in the right direction. Just a thought-

update
 

my drives are set 2.25" above the bottom of the boat and the front of the prop is 42" from the back of the boat.
we ran the boat this weekend with props turning out and it was a little better but still porpousing over 80mph. we ran 111mph @ 5300rpm 1.42 gears. with 250 lbs in the back of the engine compartment, 8 people in the boat with 60 gals of fuel on each side.

why is the extra weight helping my speed??

the more i drive it feels like the front lifts and it speeds up then the nose falls and plows and causes us to slow down. it continues this cycle at high speeds

we ran the boat with 2 people and a little more fuel only ran 109mph with 6" waves and 2' waves with a 30 mph wind porpoused into and away from the wind. no difference

help
 

:cool-smiley-027:Buy a Skater :evilb:
Hey Cody, I left him a message to call you:ernaehrung004:

The drives are too deep with that amount of set back. With large diameter blades that deep in the water you are getting too much transom lift, which throws the bow down, causing the porpoising cycle. Adding the weight in the transom is obviously holding the back of the boat down, helping to counter the transom lift, making the boat better balanced for your present set-up.

Weight sometimes can actually be your friend if you put it in the right places! The performance gains from properly balancing the boat by adding weight in the right places more than offset any losses from the additional weight itself (i.e. a well balanced heavier boat will always out-perform a poorly balanced lighter boat.) Balance, not light weight, is your goal.

Raise the drives and you should see some significant improvement in both top end speed and handling.

Tom
Total Marine

finally im getting some consistant answers...
thanks

i will need some props with some more pitch if this works

I say ,,leave the props first and take the 2 inch spacers out.

If now to high ,,,,1 inch spacers ,once u got the right hight where she runs strong ,,,then is the time to play with props to fine tune !!!!!!!!!!!!!!!!!!


I just did it backwrarts on mine ,,,LOL thats how i know !!:rolleyes:

??
 

the 2" spacers are out we will see what she will do sunday:drink:

Good luck! :cool:

Cody:

I did not realize you had spacers. My experience with these boats is limited and obviously I surmised incorrectly about the bow lift versus the transom lift. By putting the ballast in the back you did the right thing. Good luck and keep us posted.

Wannabe

better
 

i ran the boat today at Saguaro a very small lake. it seem to be better but it was hard to tell it was so rough and windy. it did 102mph @5000 with the wind and seemed smoother. im still at 7% slip so it didn't hurt my bit. i couldn't open it up all the way with a 30mph sidewind it just pushed me sideways over 95mph but it was smoother.

thanks for all the help
cody white

COOL !!!!!:ernaehrung004: ,,,7% slip ,,,hell don't change a thing the best i have ever seen was 8 % !!!!:drink:

Any updates on your baby ???:party-smiley-004:

ccat
 

:D122 mph bugs in teeth :grinser010:

Did you switch them to turn in? Green cards boat is very close to yours. Call him, he will give good input.

there turning in now and i pulled out a 2" spacer handled much better. we ran 122 mph at havasu but ran out of prop. it still has a porpus from 90-100 and on smooth water it does over 90mph

Wow, 122 and more to go. You are really smoking. The Linder Hop as it is called is characteristic of these boats in the 90-100 range. You just have to drive through it. It will be more pronounced on smooth water because the boat is trying transitioning between hydro dynamic lift and the aerodynamic lift. If the hull is freed up with less water contact with some chop it overcomes this easier. I do not know what the max hull speed is on these boats. I do know I bid on a boat in Texasin 2003 the guy had some custom built Keith Black Hemi's with Super chargers - he claimed if he put racing gas and smaller pulleys he would be pushing over 1100 hp and did `140. That was faster than I want to go.

Wannabe

Hi Cody
Call me left e mail and voice mail Pm Sent.
Thanks
Thumper

Cody, have you ever checked your location of your CG, the way you run your boat? Take a photo of the bottom of your boat at the last step.

Thanks,
MSW

Yea mine, send them back and I wiil erase this and never speak of it again

Jim
year 2 of bs

look for a 16 to 16.5 prop dia, most of the cats I know run that size.

Chris Cat @ 140
 

I still have the complete boat and would love to have you own it! Call me if your interested Mark 214 914 4700

Dry you own the boat?
-Mike

Chirs Cat owner
 

Yes I do. Call me anytime 214 914 4700

Just be aware that a set of props belong to Thumper if you checked this whole thread out. Send some pics ovr of the boat
[email protected]
Thanks
-Mike

Mike, I see your reading comprehension is about as good as your writing skills. :drink: Dry owns the hemi boat, Cody owns the other boat and is the one that porked Jim on the props. ;)

Ah couple crossed wires. I thought he was talking about the Cody boat. Though thats what this thread was all about was the Thumper/cody boat.
-Mike

Chris Cat
 

Yes I still own it and I would like to sell it.