Jack Plate

[Bomber13]

I have a 1976 Bomber Marathon 15.5' Bass Boat with a 1985 Mercury 60 (60 HP). This boat is rated for an 85 hp.<br /> With (2) adults in the boat, the bow comes up fairly high and it takes much longer to get on plane. This is with the trim all of the way down. The transom on this boat is nearly verticle so I feal that I do not have the ability to trim it down enough. I have looked for a (What I call a jack plate) stand-off bracket (As you see on the newer bass boats) that will give enough clearance to be able to trim the engine down so that on acceleration, the front end will be pushed down to get up on plane faster.<br /> I a going to add a "Doelfin" Hydrofoil Stabilizer to the engine improve the stability at WOT but I don't feel that is will make much of a difference on acceleration due to the limited trim movement.<br /> Any suggestions on this and where to find one is GREATLY APPRECIATED.

 

[JB]

Re: Jack Plate

Seems to me that a hydrofoil would certainly get you on plane quicker, Bomber.<br /><br />A set of Smart Tabs would do an even better job.<br /><br />Either would probably cost less than a standoff bracket (If they are not adjustable I call them setback brackets) and be a lot easier to install.<br /><br />This is more of a boat problem than an engine problem, so I will move it to Boats.<br /><br />Good luck.

 

[Dhadley]

Re: Jack Plate

The Bob's Machine manual plate has the ability to be assembled so it provides a negative trim angle.

 

[sangerwaker]

Re: Jack Plate

Could you use some trim shims? Sorry, I couldn't find a picture. A racer I know uses them to make more negative trim angle for better holeshot. They are basically a wedge you install between the transom and motor. I know my local dealer carries them, but I couldn't find them online. I think they were about $30.

 

[Jdeagro]

Re: Jack Plate

Tilting the motor is somewhat effective, using hydrofoils is somewhat effective for assitance in planing. However you are asking the prop to compromise it's basic job (propelling) by using it to lift the stern. And, using a hydrofoil without properly "setting up" the entire boat (ie: engine hieght, balance , motor trim) can cause more headaches than it will cure.<br /><br />We put together a booklet to help with "understanding boat balance and performance" which you can down load for Free. Go to www.nauticusinc.com then click on enter, then click on "Understanding Boat Balance and Preformance" under quick links near the bottom of the left side menu.

 

[Bomber13]

Re: Jack Plate

Thanks to everyone for the quick response. <br /> BJ - This is my first boat so I am not sure exactly what "Smart Tabs" are. How do you install them and how do they work?<br /> sangerwaker - I asume that the trim shims go where the top bolt anchors the engine mounting bracket to the transom. How far can you shim out. I am worried about the clearence between the lower end unit and the bottom of the transom when the load begins to build on the engine.<br /> nautiJohn - I understand what you are saying about compromising the basic job of the prop. I may have miss spoken concerning using the hydrofoil. My main abjective of using the hydrofoil is to obtain more stability at higher speeds. At WOT, if I hit a wave, the boat will porpose for quite a while before it settles down. On a day when there is a lot of traffic on the water, I trim all of the way down and leave it there to remain stable.<br />To all - When I first accelerate (from a stand still) and come up on plane, if I bring the front of the bopat up to where I feel it should be, it will begin to porpuse (Not real bad)and will not stop until I bring the front end all of the way down. I have been told that when the boat get on proper plane, I should here a very slight increase in RPM's and I should be riding on the back 5' of the hull. Is this correct? I have had this boat for a little over 2 years and am still learning.<br />Again, THANK YOU to everyone for your help!!!!

 

[sangerwaker]

Re: Jack Plate

Bomber13,<br />The shims actually require you to un mount your motor. They are a set thichness...enough to give you 5 degrees extra of negative trim angle. I have never heard of a case that would allow your motor to actually hit the transom, but I suppose it is possible.<br /><br />FYI-a hydrofoil will not help stability at WOT. If properly set up, the hydrofoil will be out of the water slightly at WOT. Are you running an aluminum prop? Are you correctly propped? What's your RPMS at WOT?

 

[Bomber13]

Re: Jack Plate

sangerwaker - As the transom is very near to 90 degrees, when trimmed all of the way down, the lower unit is within a few inches.<br />I am running the standard 10-13 aluminum mercury prop for this engine.<br />I cannot tell you the RPM's. I do not have a tachometer. I am planning on installing one this winter as the engine is all set up to have one.<br />Thank you for your help.

 

[sangerwaker]

Re: Jack Plate

That should be your first step. It's possible you have too steep of a prop and are not acheiving correct max RPM's. Therefore giving you a lousy holeshot. 5 degrees extra neg. trim should not cause your motor to hit the transom. I would seriously consider getting your motor correctly propped (if it isn't already) before you start experimenting with other things. Only change one thing at a time.

 

[Bomber13]

Re: Jack Plate

sangerwaker - Judging from what you are telling me, I will proceed with the tachometer first. I do have the owner's manual for the engine and it does tell me the recomended RPM's. I don't access to it until I get home from work, but I believe that is says that the engine shouls run about 5600. Does that sound right?<br />Thanks for your help. I will proceed 1 item at at time as you sugested.

 

[sangerwaker]

Re: Jack Plate

5600 sounds about right, but check the manual for sure. Getting your motor propped correcly will both help performance and the lifespan of the motor.<br /><br />Best of luck!<br /><br />If you figure out what your RPM's are, post back and we can figure out where to go from there.

 

[Bomber13]

Re: Jack Plate

Thanks alot for your help. I hope to find out in the next few weeks.

 

[Jdeagro]

Re: Jack Plate

Bomber13<br /><br />Hydrofoils don't give you stability at high speeds unless you mount one on each side of the boat. Lifting the boat from the center can only create a teeter totter effect, unless you raise the motor enough to get the foil out of the water at high speeds. Then it will do very little.<br /><br />Down load the tech booklet on "Understanding Boat Balance and Performance" then read other articles and searches, then make your choice. WWW.Nauticusinc.com

 

[phatmanmike]

Re: Jack Plate

arent you getting "nautijohns" hints........he wants you to visit his site and check his stuff... sheesh.<br /><br /><br />free advertising, who woulda thunk it !!!!

 

[walleyehed]

Re: Jack Plate

Yes, and the units are sold right here at Iboats.<br />I've tried the foils..thought they were great compared to nothing at all. Added 100 more HP to my boat (Don't ask) found the only item that makes controlability possible is a set of Mobster Tabs, also from Nauticus.<br />I'm still experimenting with fins, but not for the purpose of hole-shot....the tabs are staying on the boat. Best money you could spend right there.

 

[Bomber13]

Re: Jack Plate

NautiJohn - I did check out the smart tabs and understand now how it works. I also Downloaded the Adobe file you recomended. sangerwaker has a point with making sure I have the boat proped correctly first. I have added nautiicusinc.com to my favorites because I suspect that in the end that the smart tabs will be the way to go but I wnat to take it one step at a time.<br />Thanks again to everyone for your help!

 

[Jdeagro]

Re: Jack Plate

Boomer13,<br /><br />The suggestions (all) are good, and you do need to hook up a tach. One quick suggestion is that you can use a automotive test tach which allows for switching from 4 to 6 to 8 Cyl. just to see where you are now. Please understand that you should make the hull as efficient as possible before dialing in on the prop. If you do it the opposite, you will likely end up with a prop that is lower pitch than you need. This will cause higher RPMs than necessary, which translates into less speed at WOT, and more fuel consumption.

 

[Jdeagro]

Re: Jack Plate

Phatmanmike;<br /><br />You may not believe me but I am trying to help!

 

[Bomber13]

Re: Jack Plate

NautiJohn - I was just checking back on the post and saw your post on the automotive test tach. I had thought about that. I have used that trick on a motorcycle engine before.<br />I did want to run something by you. I understand that the smart tabs will get the boat up on plane faster. My thought behind using the hydrofoil was to give the standard foil on the engine more authority when cruising. With the front going up and down, it seems that the prop (at this time) would be angling up slightly instead of running straight when the bow is down. I am not sure if you are familiar with the old Bomber (Made by FiberKing) Marathon 15.5' but they are a stout(as in heavy and durable) It is rated for an 85-HP and with me having a 60-HP I feel that it is a little underpowered. All-in-all, the boat does real well but when I can not keep the front up, I "Feels" like the engine is working harder.<br />Walleyehed - OK, I have to ask about the 100 more HP?

 

[Jdeagro]

Re: Jack Plate

Bomber13;<br /><br />The difference between any fixed planing device (hydrofoil or trim tabs such as "step and trim") is that the lift can not be regulated. In addition the faster the boat goes the more lift they provide. Ultimately this drives the bow down too much and the result is a loss of top end. Actually two things occur, first the bow is too far down and secondly (if the boat has power tilt and trim) you end up trimming the motor out too far just trying to get the bow up. The excessive trim causes the prop to run through the water at an angle (not perpendicular) and this results in more loss of efficiency. The anti-ventilation plate (cavitation plate as it is more commonly called) helps equalize the density of the water on top of the prop so it has equal bite 360 degrees. If the manufacturers felt a larger plate would be beneficial they would design it that way. <br /><br />Unfortunately the "Old" and "common" thinking is to use the motor (prop and foils) to control boat attitude. Not a very efficient choice, and not all that effective.<br /><br />On another post, where the gentleman was determined to choose a pro before getting the boat hull as efficient as possible, I explained it this way:<br /><br />If you were dragging an anchor, would you optimize the prop selection, then pull the anchor in?<br />Assuming your boat is within reasonable range, and assuming that you are at some point going to install adjustable trim tabs of some type, I would do that first. If the trim tabs are taking care of the "getting on plane easier" issue then the prop can be one that provides the best top speed without need to worry about the planing issue.