Pacific 1925 shaft length issue

[Sjoman]

My Pacific 1925 came with long shaft motors 20” and the cavitation plates are 6-7” above the lowest point of the boat, which seems high to me. In addition on my first real day of usage I tried to trim the motors out but could barely do so before they start cavitating . I am thinking this could have been a purposeful move by the previous owner to be able to access shallow water (it was a yacht tender) but this will not work for me.
If the motors indeed are to short I have a few choices such as ;
• A bay extension kit to make the shaft length 25”.
• Lowering the existing transom (max 3”).
• Adding a lower transom bracket to the existing transom.
Thoughts ideas and opinions greatly appreciated.

[welder]

Being twins they do sit higher than a single at the keel. Is there any holes left in the mounting bracket to lower them ?
Do you have 3 or 4 bladed props?
You can also add Jack Plates , the manual ones as once you get the set they stay.

[Sjoman]

No holes left to lower them. The props are 3 blade

[MacCTD]

I would go with Welder's suggestion of a manual jack plate, be the easiest and where you only need 3" or 4" it will give you adjustment. You could also maybe sell the twins and put a single on it. I wondered about that on that boat as it has a shallow draft and the singles have 25" shafts.

[Sjoman]

I found some Jack plate’s with 6" setback from http://www.hydrodynamics-usa.com/rapid-jack.html . These are adjustable and will get the motors back and down and hopefully make a difference. I took some measurements and came up with 26" from top of transom to keel, the motors are 25" apart so 12.5 each from centre and they are long's i.e 20", with a dead rise at the transom of 14 degrees. As far as I can measure it the current position of the cavitation plate in relationship to the bottom where they meet is 2” above the bottom, so help me out please; doesn’t it appear that the motors are sitting too high.

[tazmann]

I found some Jack plate’s with 6" setback from http://www.hydrodynamics-usa.com/rapid-jack.html . These are adjustable and will get the motors back and down and hopefully make a difference. I took some measurements and came up with 26" from top of transom to keel, the motors are 25" apart so 12.5 each from centre and they are long's i.e 20", with a dead rise at the transom of 14 degrees. As far as I can measure it the current position of the cavitation plate in relationship to the bottom where they meet is 2” above the bottom, so help me out please; doesn’t it appear that the motors are sitting too high.

Been a while sense I played with outboard on powerboats but if I remember right with twins mounted on transom the cavitation plate should be even with the bottom V part of hull otherwise the prop is running in a disrupted water flow .
Tom

[goatram]

Three Rivers Marine near you sold me one of their Jackplates to Raise my motor. I bought a 30" shaft F250.

For your motors I would think about bay kits. Reason If you lower the motors to get the props to work you will also put the Power head and intake closer to the water resulting in possible water intrusion damaging the engine. A 24" swimstep would allow the engine's Cav. plate to be 2" above the bottom of the Hull

[Sjoman]

Somewhere along the line I read that for every inch you move the motors back it has the same effect as lowering them ½”. My hope is that the 6” set back on the bracket will be enough to reach the desired effect and the option of lowering and raising the bracket will be for fine tuning.

[goatram]

no it is 1" up for every 1' back.

[goatram]

http://www.thehulltruth.com/boating-for ... video.html

[wetwhopper]

I went with the "bay kit". Was very straight forward.

[JETTYWOLF]

You said 20" is long shafts??
Naw, 30" is a long shaft.

You could swapout lower units to 25" and no other b.s. would be needed. But that's expensive but "done right."

BTW, what's a Bay Kit??????

Never heard of such a thing.

[MacCTD]

You said 20" is long shafts??
Naw, 30" is a long shaft.

You could swapout lower units to 25" and no other b.s. would be needed. But that's expensive but "done right."

BTW, what's a Bay Kit??????

Never heard of such a thing.

Bay is a company that makes kits to make a 20" motor into a 25" motor, http://www.baymfg.com/

[JETTYWOLF]

TEN' FO

Never heard, because no one I know has ever had the need.

[Sjoman]

Here is an update on the slipping / cavitation issue that I experienced. After reading several postings on numerous boards I got in touch with Tom W. Clark who posts a lot on several Boston Whaler sites. His recommendation was to go with a SS prop, Stiletto Triad 3.5, rather that the stock Yamaha aluminum. In addition he recommended to go from a 11 1/8 13p to a 10 ½ 12p, not being an expert on props I thought it would be strange that a smaller prop with less pitch would solve my issue but it did. I am now able to trim the boat without slippage and gained 2-3 knots at the same RPM, my WOT went from 5,500 to 6K+ at light load and I assume my top speed (if it matters) increased as well.

[MacCTD]

Cool, strange smaller wheel, less pitch. What is the top speed now?

[Sjoman]

Not sure about the top speed, it was pretty rough when I ran it up to 6k so I shut it down right away doing 30k. My guess would be 32-34K. I will give it a try in calm seas and post the result.