fastestbowtie

First off, i know there is a prop section, but i am not a paying member (yet) and am hoping to get some answers here. This will be a long post, so I will start with what I have, then list my problems, and then my conclusions which may be wrong that is why I am asking. First I have just purchased a 1987 Checkmate Ambassadore (19.5 ft I/O open bow runabout) which was originally equipped with a 320HP 5.7 litre EFI Mercruiser with the Alpha 1 SS drive with a 1.32 ratio. The boats motor was rebuilt in 1995 including Dart heads, Crane roller cam, and other upgrades which resulted in flywheel dyno results of 424 HP, 445 TQ (not a modern computerized dyno chart, but peak HP appeared to be around 5500 rpms and peak TQ between 4500-5000 rpms). It is currently running some sort of stainless labbed prop that has had all of the markings ground and or polished off; it is a 3 blade prop with mildly cupped blades that appears to be between 13.6 and 14 inches in diameter. I did find a hand scribed "24" on the hub next to one of the blades so I am assuming it is or was at one time a 24" pitch. I made a rough measurement of my lower unit in relation to the bottom of the pad and it appears that the the center of the prop would be about 5.5-6 below the pad (keep in mind this is the Alpha SS which is supposed to be 2 inches shorter than a standard Alpha). This boat runs awesome on flat water at WOT, easily hitting 5400 rpms with 2-3 people on board and 5600 occasionally. It has not been GPS tested yet, but should run close to 80 based on previous owner claims and compared to what a suprised 25 ft Howard owner stated when we ran him (he barely pulled us and claims he was running 86). The problems are it does not like rough water, cruising, or turning. The boat does not handle rough water at all, I have to bury the trim all the way down to where it starts to vibrate and pulls the rpms down just to try and keep the bow down, if I try to give it any up trim, the rpms immediately start to pick up but then it starts to poirpose and get beat up in the rough. Even when it is smooth, if the lower unit is anything other than full down it will start to poirpose (sp) unless you get the speed up and are turning about 4000 rpms. Lastly, you can not turn at speed. If you try to turn and give it any throttle it ventilates the prop. When pulling a tube, I can barely turn hard enough to get the tube outside of the wake. I realize the shorter lower unit is not helping me with some of these problems, but am not quite willing to sacrifice that yet. I am considering a 4 blade prop which I have read will not ventilate as easily as a 3 blade (I can actually get a great deal on a new 23 pitch Revolution 4). Lastly, I am wondering if the prop i have now is providing too much bow lift (if that is possible) and that is why I am having so much trouble keeping the bow planted. Any help or suggestions would be greatly appreciated. Thanks, Johnny

mmwalters

You are not going know which is the best prop untill you find it. I think a hydromotive Q1V four blade might work. This prop tends to provide stern lift. The prop you have is a bow lifter. Call Throttle up they will point you in the right direction

fastestbowtie

Thanks for the advice... I thought about calling some of the prop guru's, but then saw that most of the ones I would have called post on here anyway, so I was hoping this post would get some feedback from them as well as possibly some feedback from some of the other guys on this board with 19-21 foot high HP boats. I realize it is hard to nail the prop perfectly the first time, but then again I have a very tight budget and will have to either nail it the first time or at least get close enough to live with.

abones

Where are you located? and did the boat come from the Michigan area? If so take another close look at the prop to see if any other marks or identifications are engraved on it. It sounds like it could have come from Action Marine. If it did that might explain a lot on the Prop/set-up etc. My first checkmate came from there, extremly fast but had the same symtoms.

fastestbowtie

The original owner was in Connecticut, he sold the boat to a man down here in Austin Tx in the mid to late 90's (1997 or so), this guy took care of this boat like it was a 63 Vette or something. Unfortunately, he passed away a year or so ago and his wife was not comfortable with the boat so i bought it from her. I have no idea, if this prop has been on there the whole time it has been in TX or not. It does show some signs of wear, and the skeg is showing considerable wear. The leading edge of the skeg is completely flat where it looks like it has been impacting something very uniform over and over (maybe like a cross bar on a lift or something), there are not any deep gouges or indentations, but you can see and feel where the aluminum on the front edge has been rolled over.
One thing I have noticed about the prop on the boat is that the vent holes on the side of the hub appear much smaller than those I have seen in the pictures of Mercury Marine props, of course in this application they are plugged since this boat has through hull exhaust only.

fastestbowtie

I know this post is from last week, but since the holiday weekend has passed I was hoping it might get some new responses... perhaps from one of the reputable prop shop guys/gals. One thing to add is that on another forum someone with a hull very similar to mine with a big block and Bravo 1 drive recently installed a Hydromotive 4 blade prop (he called it a stern lifting prop, but from what I have seen on their website it is just a neutral or full hull lifting prop) and has had very good results with it. He claims it rides much better, handles the rough better and lost no speed. What do you all think.

East Coast B

On that small of a boat, I don't see any need for blade cupping. A 4 blade will give you more stern lift. As for losing no top speed, well that is boat/power dependent. You will definitely loose rpm going to a 4 blade, but if the boat has enough power and is hitting a rev limiter, a person going to a four blade might not notice the decrease in rpm and speed only because they were propped incorrectly to begin with. If a boat was pretty much matched to the correct prop, going to a 4 blade will show a decrease in rpm and speed... hope I described that correctly.

Keep checking around with people in your area and shops that sell props. I've seen places that will agree to taking your payment for a prop, but let you try different sizes knowing you'll take one from them. You'll pay more than if you shopped internet, however the extra money will get you the testing and knowlege of what will work best for your boat....

Good luck!!!

bbladesprops

Nice talking to you. Hope we gained some information together!