nedd help ?jack plate or not

crabguy

Recruit
Joined
Sep 7, 2009
Messages
4
helllo guys hope every ones haveing a good day? ok here it isi have a 1965 15.5 starcraft aluminum boat and have a 1973 50 hrs evinrude short shaft motor and my transom is 21infrom top to bottom im new at this so i took the boat out yesterday with a new prop 13 3/4x15 thinking that it would fix it and it worked ok not like i hoped (the old prop was the same thing but the prop was spun) ok out of the hole wot the prop dosent catch but if i go slow throtleing up it will work i make turns and no slipage that i can tell will putting a jack plate help or not. and if i lower it it might put the exaust in the the water is that ok here are som pics
 

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hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: nedd help ?jack plate or not

Guy, you don't need a jackplate, just a better prop. But you didn't give enough information for me to know what prop you need.

If you will fill this out I will help you.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for $ 50
RPM ___________ Speed ___________ No. of people ____________ Gal. Gas ________
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

It would be good to have a couple of pictures of the transom and motor so I can see how high the motor is and where the anti ventilation plate is compared to the bottom of the boat. Here is how to take the picture.

Anti Ventilation Plate

AntiventilationPlateStraightEdge-2.jpg


I would also like a couple of pictures of the stern from the side of the boat taken from down low with the anti ventialtion plate parallel to the keel using a straight edge on the keel reaching to the anti ventilation plate to see if your motor is too far down on the transom, here is how to do it. And one picture down low from about 2' behind the motor as well so I can see the hull form at the stern.



H
 

crabguy

Recruit
Joined
Sep 7, 2009
Messages
4
Re: nedd help ?jack plate or not

ok i can ansewer som of the ? 1.1965 starcraft runabout 2. 15.5 ft 60 in transon bouat wieghs about 600 lbs without motor im guessing there is no plate on the boattelling max persons and so forth 2a. not shure 3. 2-3 ppl and 6 or so gallons 4.fishing and mabe pulling a tube if i can 5.it is not a deep vee 6. 1973 50 horse evinrude 50372A 7. not shure yet 8. 5000-6000 rpm 9.4in above bottom of boat i used a board like u asked 10.not a bass boatnot shure if padded 11.its a rebuilt aluminum 3 blade prop 13 3/4 15 pitch 13. i dont have a tach yet (the prop i got with the motor was spun so would not get me on plain but it was an aluminum prop to 13 3/4 x15) and dont have a spedometerwehn i got up on plain iwas doingi would say 35mph 2ppl in the boat and 6 gallons of gas 14. 2000 ft above sea level 15. not tuned but has new plugs 16. one day 17. rebuilt aluminum prop 18.ok when i go wot from a stop it will go for a bit and then act like i spun the prop but if i go slow from a stop it willget up on plain i dont notice any cavitatoin but not shureas im new to this i would like to go wot from a stop and have no problems
 

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hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: nedd help ?jack plate or not

LOL, I lied, with these pictures I can tell you you have the wrong shaft motor for that transom. The anti ventilation plate is too high above the bottom of the boat and this will cause the prop to ventilate. If it is 4" too high now you need to cut the transom down about 2"where the motor goes or get a longer shaft motor for it to work correctly.


H
 

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,306
Re: nedd help ?jack plate or not

your motor does not fir your transom...

you probably have a 21" transom on your boat and you have a 15" shaft motor.

your cavitation plate is WAY high!!!

but to answer your question a jack plate could solve your problem and it might be easier than buying another motor

you could buy a fixed jack plate for a hundred bucks or so, maybe and , if you measured carefully bolt it on at the right hieght to mount your motor where it needs to be.

or you could buy a manually adjustable jack plate...

there are usually a few set of holes on the motor and a few set on the jack plate...


as stated before...the large flat "wing" on the lower unit, called the Cavitation plate, needs to be close to level with the bottom of the hull!!!!!

good luck

bob
 
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