Jack plate worth the $'s on my boat?

[vissertrades]

Hi,<br /><br />I'm considering a manual jack plate for my 15' '84 Smokercraft "Big Fisherman" (Deep semi-V, aluminum, console, 15.5'). It has a '95 Johnson 50 on it and I'll be running a Stiletto 17P prop. The boat has Smart Tabs installed (gas spring assisted tabs) and the boat tends to be bow heavy. I realize the "x" dimension adjustabiliy factor will be a plus, but I'm wondering if the set back part of the jack plate would be of any benefit on my boat? Please advise on set back dimension if you think my boat would benefit. Also, would set back have an affect on the position of the boat (attitude) while still? Motor has TNT and current prop will ventilate fairly quickly as I trim out, I haven't tested the boat with the Stiletto prop yet, it's supposed to really bite the water and be a better bow lifter than my OMC SST prop. The boat was real sensitive to the trim tab adjustments and I ended up reducing the actuator load to eliminate plowing. I know I'll need to dial in the "x" dimension this spring so I was considering a jack plate with the added benefits of set-back...<br /><br />Thanks!

 

[LubeDude]

Re: Jack plate worth the $'s on my boat?

Jack plates nearly always offer some advantages over stock, but I would think it minimal with just 50HP. Why is your boat "bow heavy"? Could you shift weight to the back?<br /><br />You need to know what you are experiencing first.<br /><br />Cavitation: The formation of “voids” or air inside the water stream, caused by low pressure near a surface. Encountered when the water separates from the propeller. Also called “ventilation”; causes propeller burn, and can lead to “blow-out”.<br /><br />Blowout: occurs when the ratio of air to water around the propeller gets so high that the propeller is no longer grabbing water, but is trying to propel itself through air (or a relative vacuum). This causes the propeller to lose "bite", and then a chain of events occurs that can range from merely a "loose" steering feeling, to a vicious turn to the right (typically). The speed at which this occurs varies with boat design, gear case design, and propeller design.<br /> <br />Anti-Ventilation plate: The horizontal web or plate above the Lower Unit. It is intended to prevent the Prop from sucking surface air, Ventilating, into it and causing a Cavitation like effect. Useful on a deeply mounted outboard or drive unit. On high-performance or surfacing setups, it is of limited value due to it being out of the water while on plane. <br /><br />If you are having a ventilation problem, your engine is too high already! A setback may help this.

 

[Bondo]

Re: Jack plate worth the $'s on my boat?

If your boat is Plowing, <br />Loose the Spring loaded Trim Tabs.......<br />Those are for Lifting the Stern.......

 

[Jdeagro]

Re: Jack plate worth the $'s on my boat?

Pete;<br /><br />Bondo is almost correct, it seems you have too much lift at the stern. If you have already reduced the trim tab pressure by the standard adjustment, then we will exchange the actuators, at no charge, to a lower pressure. Call me so that we can get the set up correct. 800-233-0194

 

[vissertrades]

Re: Jack plate worth the $'s on my boat?

John,<br /><br />I have gone from 40# to 30# actuators but havn't tried them yet. The 40# set at weakest point was scrubbing off about 1 Mph. I do like the low speed plane-ability. Once boat is going on plane the tabs exert enough force to keep them compressed, not sure if it's 30#/cyl. Whatever this force is it seems that it could be counteracted or overcome via set-back (kinda like balance on a teeter totter but with fulcrum being boat center of gravity)? That would be one advantage of the jack plate, plus height adjust and cleaner water. My boat has 2 bow seats that are used often, this is a major component of the "bow heavy" condition I stated. This spring I will be experimenting with a Stiletto propeller (round ear extended cup) that should produce more bow lift than my OMC SST did. I will dial in actuator position on the tabs. I'm really leaning towards a jack plate so I can tune engine height as well increase bow lift.

 

[LubeDude]

Re: Jack plate worth the $'s on my boat?

Seems like you are fighting a loosing battle with the trim tabs acting against what you are trying to achive.

 

[Jdeagro]

Re: Jack plate worth the $'s on my boat?

If You have not tried the 30# actuators yet, and you are loosing only 1 mph, it will take very little adjsutment to get to the point where you pick up 2 mph. Once at this point you will have both the low end performance, and the extra top speed. I am sure you are also getting a much better ride and tracking. Stay in touch!

 

[richg99]

Re: Jack plate worth the $'s on my boat?

Nautijohn, I don't know if you review or scan the boating Usenet newsgroup known as Rec.boats or not, but this evening there is discussion/query by one guy about Smart Tabs. you might wnat to jump over there and join in. RichG

 

[Jdeagro]

Re: Jack plate worth the $'s on my boat?

Richg99;<br /><br />Thank you, I will do that.