Cheeckmate Diplomat

[Mark]

Bill
I saw your mate on boattraderonline. It is the exact same boat as mine. Even the color. Yours is in beautiful shape by the way. I am amazed you can get 60+ mph out of her. My bow does not come up like yours even when trimmed right up. Do you have any trouble with porpoising or chine walking? Do you have to lower your jackplate to ski? What size and type motor would you recommend for when I repower? I'm also concerned about stress on my transom. It seems solid but has gel coat cracks in the corners. They don't seem to be growing but are blacklined.
Mark

 

[Shameless]

Mark,
The lower I go with the motor, the more it wants to chine walk. I have spent many hours finding where to put everything in the boat when I go out to keep the weight centered. I am sure you know, this boat is VERY weight sensitive. Also, with chine walk, sometimes it just takes a little extra white nuckles and practice to drive through chine walk. I used to take the boat out 4 to 5 times per week alone and push the boat to learn steering techniques for this hull. I did it alone so I would not scare anyone except for the people on the shore. I boat on the Mississippi River where people do not really ski so I can't answer that. I can tell you that the height I keep the motor at never showed signs of cavitation, even while in hard turns at 50 mph. I actually would have liked a little more ventillation when getting on plane since I am turning a 24p Raker. The boat takes about 3-3.5 seconds to plane which I consider a little slow for such a light boat. Porpoising, never. I do have a plate mounted to the cavitation plate, not a whale tail though. I got it from Overton's, but do not remember the name. It worked great to keep the bow down when the water got rough and kept the boat on plane down to 13mph. When you repower... Since noone makes a 140, I would put on a Merc 135. If it was me, I would stay away from the optimax. It is a great motor, just not for your application and not worth the extra money. Do not let anyone talk you into putting a 150 or bigger on the boat. With as sue happy as everyonr is now a days, if you hurt someone, you will lose everything you own and could own for the rest of your life. It happened to someone I know. Yes, I am getting alot out of the little boat, but I probably have 200+ hours in working on the set-up. You can achieve spped out of the boat with lots of time and patience. You can either check with Rick from Bayview Marine or myself about the bottom of your boat, but it sounds like you might have a hook in it. Where the boats sits on the trailer is very crucial. My e-mail is fischerbill@msn.com if you want to ask any other questions and do not want to do it over the forum.
Happy turkey day!
Bill

 

[Shameless]

Mark,
Something I forgot to mention that will cause to to not be able to drive through chine walking is loose steering. Check to see how much play is in the wheel. The more play, the harder to drive. When you repower, definately relace the steering cable or if you go with a new motor, have it rigged with dual cable steering. If you take notice, all high perf boats should have at least hydraulic steering or even better yet hynautic steering, both of wich are expensive. With boats like our, I do not feel it is worth the coulpe of thousand dollars to convert to hydraulic steering. As far as your cracking transom. It is pretty much inevitable with outboards. A must is to make sure the motor is supported someway while trailering. That is when the transom really take the abuse, when the motor is in the up position and bouncing down the highway at 75mph. You want the motor as close to vertical as possible leaving enough clearence so you do not drag your skeg.
Later
Bill

 

[Shameless]

Mark,
I went and looked at my boat today and the plate I mounted on the motor is call "The Edge" When running at spped, it does not slow me down because it is out of the water.
Bill

 

[175checkmate]

Bill is right, the hardest thing on a transom is when its on the trailer. If you do not have one pick up a trailer buddy. This is a support that runs from the foot to the trailer to help support the load when going down the road.

1975 Checkmate Tri-mate 2, 2.4 200+

 

[frank812]

Propeller Size
The size of a prop is described using two sets of numbers. These correspond to the diameter and pitch. The pitch always follows the diameter when describing a propeller.

Diameter
The first number listed in a propeller size. Diameter is defined as two times the distance from the center of the hub to the tip of the blade. It can also be looked at as the distance across the circle that the prop would make when working.

Pitch
The last number listed in a propeller size. Technically speaking, pitch is the theoretical distance a prop moves forward in one revolution - assuming there is no "slippage" between the prop blade and the water. In the real world, there is some slippage and therefore the distance advanced is less than the design pitch. Pitch can be visualized as the tightness or looseness of the blades as they swirl around the prop hub. If the blades appear tightly wound and angled sharply inward toward the hub, the pitch is high. If the blades appear loosely wound and angled outward from the hub (that is, they appear flatter), the pitch is low.

Cupping
Many of today's propellers incorporate a cup at the trailing edge of the propeller blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases. A cupped propeller also works very well where the motor can be trimmed so that the propeller is near the surface of the water. The cup will typically result in higher top end speed on one of these applications.

Ventilation
Air from the water surface or exhaust gases from the exhaust outlet being drawn into the prop blades causes ventilation. When this situation occurs, boat speed is lost and engine RPM climbs rapidly. This occurs most often with high transom mounting, over-trimming the engine, and sharp turns.

Cavitation
Cavitation (which is often confused with ventilation), is a phenomena of water vaporizing or "boiling" due to the extreme reduction of pressure on the back of the propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can result in metal erosion or "cavitation burn" to the prop's blade surface. There are numerous causes of cavitation such as incorrect matching of propeller style to application, incorrect pitch, physical damage to the blade edges, etc.

Rake
Rake is the degree that the blades slant forward or backwards in relation to the hub. Rake can affect the flow of water through the propeller, and has implications with respect to boat performance. Aft rake helps to trim the bow of the boat upwards, which often results in less wetted surface area and therefore higher top end speed. Aft rake propellers also typically "bite" better on ventilating type applications. Forward, or negative rake, helps hold the bow of the boat down. This is more common in workboat type applications.



Selecting the Right Propeller For Your Boat and Engine

The best propeller size for your boat and engine combination is based on the recommended operating range at wide open throttle (w.o.t.) for your engine, which you will find in your operator's manual. This will be expressed in terms of a certain horsepower at a certain RPM (revolutions per minute).

The goal in prop selection is to determine what propeller style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum RPM where maximum horsepower is produced.

Run the boat/motor at w.o.t. under normal operating load to determine the maximum RPM you are able to obtain. A tachometer is necessary for this test. Adjust the motor trim angle for the optimum performance. If during this test, you begin to exceed the maximum rated RPM of the engine, reduce throttle setting to a position where maximum RPM is not exceeded.

If your test results in your being able to over-rev the engine, you need to increase the pitch of the propeller. Increasing the pitch increment by 1" will result in approximately a 200 RPM drop. If your testing shows, however, that you are only able to obtain a RPM somewhat lower than the maximum rating given by your engine manufacturer, you would need to decrease pitch. Decreasing pitch would increase your RPM.



Example:


Operating Range = 5000-5600 RPM
Top End of Operating Range = 5600 RPM
Tachometer Reading = 4800 RPM

Difference = 800 RPM


For every 1" of pitch size, the effect will be approximately 200 RPM. Knowing this, take the difference in the above example at 800 and divide it by 200. The result is 4. The prop to use will be 4" in pitch less than the prop that was used.




Switching from an uncupped to a cupped propeller will also reduce your RPM. The cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200.

Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. If you use your boat for fishing, cruising and skiing, one prop probably won't do all three things equally well. It is best in circumstances like this to have two propellers. One to accommodate one set of circumstances and the other to perform best under the different load. It could, in fact, be that more than one propeller would be suitable for your boat and motor combination depending on your usage. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer

 

[175checkmate]

Great information Frank,
I will add abit

Diameter. When increasing diameter. General rule: For every inch increase, go down an inch in pitch.

3 blade vers 4 blade.
If you have a 3 blade and you are switching to a 4 blade You drop 1-2 inch of pitch.

These are all FYI, Each type and style of prop handels differnet.
The best advice is to try as many props as you can beg and barrow to see what works on your boat.

1975 Checkmate Tri-mate 2, 2.4 200+

 

[Shameless]

Mark,
Are you still around? I was in a local Napa today and saw Liquid glass. If you are still using it on your boat, stop! It sais on the front, for non-porous finishes. That is why you gel is fading quickly, you can't seal gel or it will fade. That is an automotive wax/polish. Gel is porous and needs to breath. That is a big differance between auto polishes and marine polishes. It is a fine line, I know, but trust me on this.