Prop and other help needed 28 Saber 1989
 

I've had a hard time getting my Saber to run flat at speed. It has a bad porpoise that keeps me from dragging the tab at pretty much all speeds. Would like to be able to run WOT without having to drag my tabs. Unfortunately I've not been able to get any real top speed numbers to calculate current slip % because I'm having to drag my tabs. It has twin mercury black 502/415 EFI mags with standard bravos 1.5


It is a 1989 28 Saber, hull #3. The first one made with twin engines. It's like the twin engines were squeezed into a narrow 8ft beam single engine boat. The chines are tiny, about 1 1/2 inches wide. Subsequent models were changed to widen the chines and engine bay quite a bit. There is a ton of rocker in the hull, like 2 inches worth, the corners of the hull don't even sit on the trailer bunks there is so much rocker and it begins about 2ft forward of transom.


Initially I tried a pair of bravo 4 blade 26p props. The porpoise was terrible. When I say terrible I mean it was violent and would develop faster than I could react. I put on 3 blade mirage props 25p and saw significant improvement, porpoise developed slower so I could react to it, but still too violent at speed when trying to raise the tabs. The prop center shaft is at 6 1/2 inches below the hull, I'm certain. The boat is very sensitive to changes and weight it seems. I am going to play around with center of gravity (weight) and turning props in; the props are currently spinning out. We are going to try moving weight forward or back. Original power was 454 merc 365hps I think and original owner said it didn't have these kind of issues. I bought it as a completely rigged hull less motors. The only change in weight from stock setup is that the exhaust manifolds are now IMCO so aluminum instead of cast iron. There are also two separate 45 gallon fuel tanks that sit in the cabin on top of the stringers just in front of the cabin bulkhead held in place by an extra bulkhead on the forward side of the tanks. Any help would be greatly appreciated and thanks to all who contribute on this site.

I'd try a set of Hydro Q4's

Thank you, in what size? 27p?

Somewhere in that range.

I'd try a lower pitch Q4. Hydro's seem to be a pitch or 2 higher compared to Bravo's. They always seem to knock the dick off the RPM's when I have ran them.
Have you contacted Doug?

Porpoising is caused from high bow lift, boat attitude change, then stalling of the lift. Very similar to aircraft.

Hull rocker is going to add to the bow lift.

CG is a dynamic balance that moves aft the faster you go.

What tabs are you running? How much speed are they scrubbing to keep the bow steady?

As Griff mentioned, props are one of the easiest tuning methods you have. Turning out and using props that reduce bow lift.

+1 more for a hydromotive quad 4. 27p mirage or mirage + would also be worth an experiment. I was never able to gain the speed at 6-6.8" below the bottom with anything but 3 blade top speed wise. The hydros were always close. If you don't plan to change the x dimension I would certainly procure a set of each. Likely 26p Hydro will be what you want.

I think the hydromotives are probably the best suggestion before you start trying to get the drives out of the water. With all that rocker and all that leverage its just a see saw. You want to push it and let the boat naturally lean back on the rocker.

Thanks guys, really appreciate all the thoughts. Lots of 28 saber guy's have had luck with -2 shorty lower units, but want to try the props and weight first to rule those out. I bought (12) 25lbs bags of steel shot to play with over the holiday going to try moving some weight around. Was playing around with google AI and research indicated the 502 mag/efi's are about 210 lbs heavier than the original 454 setup, which I presumed was carbed. That is an extra 420lbs of weight. Then we used Imco exhaust manifolds, which AI indicates is 80lbs lighter per engine, so we shed 160 lbs there. Then we added a light aluminum swim platform with ladder, I figure that is about 40-50lbs. So net, net I am about 310 lbs heavier in the stern. That's a lot of extra stern weight for a narrow and sensitive boat.


Any ideas on how to remove or counter added weight to stern to try to get back to the stock weight/center of gravity? Lithium batteries? Remove silent choice exhaust (don't like that idea)? Add weight to middle of boat?

REVOLUTION 4 props might Be worth to try, those have amzing ammount of lift. Dont Be affraid The small diameter.