15' Checkmate Prop

[largecar91]

In 72 the biggest would have been Mercury 140. As Checkmates progressed thru the years they got heavier because of more comfort features. If you look a brochures thru the years look at the weight and hp ratings.

[W2F a V-King]

Not sure how boats were rated back in the 70's....Never paid much attention to what was recommended .

But here is a link to how they are "supposed" to be done per certifications today. This is not the actual US Coast Guard page, but does show their formula.

http://newboatbuilders.com/pages/hp.html

Basic formula is :

Boat weight is not factored in as far as I can see. But that only makes sense.... a heavier boat needs more power to go...seems that should factor in somewhere...

Example 1: Bow Rider - Length = 19' 6" Transom width = 84" remote steering and 20" transom height.
(Length x Transom Width X 2)-90 = HP = ( 19.5 X 7.0 X 2) - 90 = 273 - 90 = 183 (136 KW)
Horsepower = 185 (138 KW)

Which seems to work for the two project boats I have right now.
175 for the Viking
163 for the Vector

James

[Go Tast Get Wet]

I have a quicksilver lightspeed 13 1/2 x 24 like new in the box I got to try on my checkmate predictor if you're looking for a cheap deal. Right now I am running a spitfire X7 SS 21P 4-Blade.

[bearclaw]

My '70 MX-18 was stamped for 160 hp. I think the Coast Guard rewrote the reg calculations in '72 or '73. Before that, they took into account whether the boat was decked over or open, and mfgr's got away with murder. A 10-ft rowboat might only have a rating of 7.5 hp, but my '73 10-ft Playmate was stamped 50 hp, and the older style (1970) were stamped 55 or 60. I saw a "comp" version of a 1970 Playmate that was stamped 80 hp! I never saw an MX-14 that had over 100 hp on the plate, but anything was possible back then. Everybody put 1500's on the 15's, but as I recall, there were a couple "mishaps" (not really boat/motor combo-related, but a guy hit a buoy at high speed, and two lost the guts out of their short 1500 gearcases from the stress). All of a sudden it started getting really hard to insure them in my area.

[largecar91]

My mx 14 was a factory race boat so maybe that is why the 155 rating

[flatbackcanoe]

The laser is a really good prop. I use a laser on a 14' sidewinder (bow tank) with an 88 115 inline.
Even if it doesn't end up being your fastest prop, which it might be, you'll be happy with it.

[Rocketsled]

Out of curiosity-how do exhaust-over-the-hub props work? At first blush (conventional thinking), exhaust gas past the blades sounds incredibly bad!

-Dave

[Rocketsled]

In 72 the biggest would have been Mercury 140. As Checkmates progressed thru the years they got heavier because of more comfort features. If you look a brochures thru the years look at the weight and hp ratings.

I stand corrected. Off to the Merc hall of shame I go. . .

-Dave

[Rocketsled]

I have a quicksilver lightspeed 13 1/2 x 24 like new in the box I got to try on my checkmate predictor if you're looking for a cheap deal. Right now I am running a spitfire X7 SS 21P 4-Blade.

I'd give it some honest thought. Get back to me. PM if you can.

-Dave

[W2F a V-King]

Out of curiosity-how do exhaust-over-the-hub props work? At first blush (conventional thinking), exhaust gas past the blades sounds incredibly bad!

-Dave

Generally speaking...and I say "generally" because in my experience, what one prop does on one boat, the same prop will likely do different on another boat.

Over the hub propellers do use exhaust gas to cause a lot of slip on acceleration, allowing quick rpm build up, but once up in the rpm's, and when the prop bites they grip like any other through hub. Once up in the power band of the motor, and the prop bites...there usually follows some awesome acceleration!!

Also..depending on boat and set up, over the hub props "usually" are meant to be surfaced, or raised enough to expose the tips of the blades out of the water as they swing around the top side...."usually" !!

If the boat is light enough, and the motor has enough ( allot ) of power, the amount of slip is negligible. Look at drag boats for an extreme example.

On a fishing or ski boat though, or a general purpose boat, for the "Most" part a through hub prop will give the best "all round" performance, giving better take off and low rpm planing, with "maybe" some top end sacrifice. May even help keep the boat on plane at lower speeds.

Which is why a lot of people have several propellers for their boat if they want to do different types of boating...Top end speed...low rpm grunt to pull skiers... etc...

These are my opinions, and others will likely have other experiences...

Hope this helps some.

[bearclaw]

Yes, most of the props mentioned here are meant to be surfaced - especially the over-the-hub props, I don't even know how they would react if buried in the water.
So if you have a long shaft (20") motor, which I assume you do, then your setup has to be adjusted to compensate for that, i.e., raise the engine via a transom plate, transom jack or setback. You'll want to be up at least 3-3.5" or so to start out with. You will lose torque on takeoff - it will not be a ski boat with that setup - but once you plane off, it will bite and you'll be off to the races. That's the only time that weight in the bow would help you, in planing off. Once you plane off, you'll want that weight in the tail, without going to extremes of course. It's all about reducing wetted surface. Those boats do have a pad, not like an Allison's, but it's there and you can get up on it. It takes power and the right setup. When you start getting the lower unit out of the water, you'll free up the prop and begin getting it to run like it should, you'll reduce the amount of motor dragging in the water, and that will also help the handling a LOT (tendency to chinewalk). Decades of fiberglass curing and sitting on the trailer also guarantee that you have a decent amount of hook in the bottom. Take a long straightedge and hold it up to pad, parallel to the length of the boat. Check for gap between the straightedge and the bottom. More than 1/16" gap, and you're feeling the effect. It's pushing the bow down. You can sand that out, if you get really ambitious.

From there, try going up higher (watch your water pressure, but you should have no problem), watch the tach (TOP's like to be wound freely, 5800-6000 rpm min, except for that goofball de-tuned 90 hp. 900 in the late '70's, that ran out of wind at around 5000 rpm), and play with props. Blowover at those speeds is highly unlikely, BUT if you have power trim, don't get silly with it. All it does is throw water up in the air and make you less efficient.

Try some stuff, and have fun!

[Rocketsled]

Yes, most of the props mentioned here are meant to be surfaced - especially the over-the-hub props, I don't even know how they would react if buried in the water.
So if you have a long shaft (20") motor, which I assume you do, then your setup has to be adjusted to compensate for that, i.e., raise the engine via a transom plate, transom jack or setback. You'll want to be up at least 3-3.5" or so to start out with. You will lose torque on takeoff - it will not be a ski boat with that setup - but once you plane off, it will bite and you'll be off to the races. That's the only time that weight in the bow would help you, in planing off. Once you plane off, you'll want that weight in the tail, without going to extremes of course. It's all about reducing wetted surface. Those boats do have a pad, not like an Allison's, but it's there and you can get up on it. It takes power and the right setup. When you start getting the lower unit out of the water, you'll free up the prop and begin getting it to run like it should, you'll reduce the amount of motor dragging in the water, and that will also help the handling a LOT (tendency to chinewalk). Decades of fiberglass curing and sitting on the trailer also guarantee that you have a decent amount of hook in the bottom. Take a long straightedge and hold it up to pad, parallel to the length of the boat. Check for gap between the straightedge and the bottom. More than 1/16" gap, and you're feeling the effect. It's pushing the bow down. You can sand that out, if you get really ambitious.

From there, try going up higher (watch your water pressure, but you should have no problem), watch the tach (TOP's like to be wound freely, 5800-6000 rpm min, except for that goofball de-tuned 90 hp. 900 in the late '70's, that ran out of wind at around 5000 rpm), and play with props. Blowover at those speeds is highly unlikely, BUT if you have power trim, don't get silly with it. All it does is throw water up in the air and make you less efficient.

Try some stuff, and have fun!

Smoking awesome post Barry, along with everyone else's.

I scored a 24p Laser AND a 26p small ear chopper today. After the engine is broken in, I will work my way up to the chopper with lift and the aim to get on the pad and the prop to surface. I want it to LAUNCH!!

[Rocketsled]

Updating an old thread. To recap-15' Checkmate hull, 115 ADI L6 Merc, Anti-Cav plate a conservative 3" above the little pad. Tried out a 24P Laser II. 58mph, not too bad if it doesn't chine walk first. The Laser bites a little past cruising speed, like an automatic transmission shifting into overdrive. I'm impressed. Trying a 26P chopper this weekend.
-Dave

[capt911]

Updating an old thread. To recap-15' Checkmate hull, 115 ADI L6 Merc, Anti-Cav plate a conservative 3" above the little pad. Tried out a 24P Laser II. 58mph, not too bad if it doesn't chine walk first. The Laser bites a little past cruising speed, like an automatic transmission shifting into overdrive. I'm impressed. Trying a 26P chopper this weekend.
-Dave

Just read this whole thread as I have a 1972 MX16 with a 135 2.0 Black Max. It came with a 21p stainless way to low in the water I since had a 13.5 x 23 Laser II recommended and bought one, have raised the engine and playing with that. So far so good have not had the time to raise it more actually thinking of putting a jack plate with minimum set back to play with the height when time allows.

I have some tuning and Carb work to do first but would be interested even though we have different engines our hulls are very similar to hear how you make out and what props. One of my main concerns is how high I can go and still have adequate water flow. I put a water pressure gauge and others have recommended and temperature gauge as well. I epoxied the top couple of intake holes and taking it higher a little at a time. I would like to see you post your results as you play with props or PM me. I will do the same as I move ahead with mine. Good luck


On another note I saw HP ratings discussed earlier in this thread, I had I believe was a 1969 V141 one of the original style mates and it had a HP rating of 150 on it back then