Offshoreonly.com - Drive height, prop slip, speed, add boxes? questions

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- Drives and Lower Units (https://www.offshoreonly.com/forums/drives-lower-units-217/)

- - Drive height, prop slip, speed, add boxes? questions (https://www.offshoreonly.com/forums/drives-lower-units/252536-drive-height-prop-slip-speed-add-boxes-questions.html)

Quote:

Originally Posted by jeffswav (Post 3396785)

It could be that you are getting your terms mixed up. Some people interchange x-dimension and propshaft depth. The x-dim is the relationship of the bottom of the boat and the crankshft centerline of the engine. The propshaft depth is the measurment of the bottom of the boat to the center of the propshaft.
It sound like your drive is too high causing too much slip. You could get a spacer, try a 5 blade prop or try a standard ext box with no raise.

Before you do anything how deep are they now? If you do not know get a measurment. Before you know this information you are just guessing.

Ok I finally got my info gathered this weekend. With the lower units trimmed all the way down and putting a level with the bottom of the boat at the lowest point, the prop shafts are 3 inches lower than the boat.

With the lowers trimmed up to 3 they prop shafts are higher than the bottom of the boat. when driving, trimming the lowers up any higher than 3 starts to make the boat hop.

Thanks for any help

Quote:

Originally Posted by Nmca_chevy (Post 3415693)

With your drive trimmed so that your prop shaft is parallel with the running surface. How far is the distance from the prop shaft centerline to the running surface? This is measured at a straight angle from the running surface or prop shaft. That is the needed info.

Also

Jeffsway.

I'm not sure I understand your explanation. The x-dim is used to determine the depth of the propshaft. As you know, the B1 has an distance of 21.13/16" from input to prop shaft centerline. So if the distance is fx. 17" from crank/input shaft center line to bottom/running surface (x-dim), your propshaft depth @ centerline is of course 4.13/16". Not calculating any transom angle deveations.

Quote:

Originally Posted by Nmca_chevy (Post 3415693)

You really need to get the drives trimmed so that the propshafts are parallel with the bottom of the boat and then take some measurements for the depth. Different indicators are numbered differently so its hard to tell exactly what you have going on.

What do you mean by "hop"..... maybe porpoising????

I finally got around to addressing this thread - sorry for the delay. I originally rigged the boat with the Pulsedrive (with the help of someone local that knew what he was doing). There were many positives to this setup, but the hull just did not like it when it came to top speed. To make the Pulsedrive work the motors were located as low as possible in the bilge. The rear seating is over the top of the motors - another reason why the motors were installed so far down.

The boat was re-rigged with XR's and -2" IMCO lowers. This improved the top end ride significantly.

I wish the boat could have used Eddie's Hp more effectively on the top end. The Pulsedrives were bulletproof, and the mid-range acceleration with #6 props was incredible.

I should be able to get those messurments better this weekend.

I am just trying to figure out why this boat has so much prop slip (like 30%) with online calulators.

Frequencey, what were you top end numbers? The boat will only go 68mph. it will go 68 on glass or in the roughtest water. no more. With that power it should run low to mid 80s.
It has 28 labbed 4 blades.