Prop, Porpoise, Boat Balance Convincor

[wca_tim]

What's your take on a labbed Mirage? The previous owner of my boat sent his back to Merc for massaging and many $$$ later swears speed and ride wont get any better

Don't have personal experience with that one. I run a mirage for all around use on my boat now (because it was cheap, available and in the right pitch), but A. I have smartabs on it (NO loss of top end, planes a lot faster and a lot lower speed than without) and B. my boat is smaller and porpoises a god bit, especially in the mid range, with bow lifting props.

I suggested a bravo because less bow lift and different blade design than a mirage. That and highly recommended by a number of people I've talked with. Based on the playing I've done so far with my boat now, I'm going to try one as soon as I can find a good price on one or borrow one in the right pitch range.

The hydromotive is even more of the same (ie neutral / stern lifting). So far, my boat is fastest with a Hydromotive quad iv on it... and the most solid feeling at wot... that's with the prop shaft burried 7 1/2 inches below the pad...

 

[Mark A]

From what I have read on boards like this it seems the Hydromotive is the best performing prop for this hull due to its high stern lift. The Bravo is also highly reccomended but I hesitate to purchase either without a trial (both are pricey) and there are none in my area available to test run

I think too that the Bravo's smallest pitch (22 ?) would be a size or two too much for the boat.

I have a Powertech (www.ptprop.com) dealer that will let we swap props from his stock until I find one that works best but I have to purchase a prop. They are very reasonably priced, have a huge selection and the limited reports I have read on them seem positive. They have 3 and 4 blade props that are designed with a lot of stern lift. I might try these on this weekend coming up.

Has anyone had any experience with Powertech props? I am very curious about anyones experiance with the Enertia prop too.

 

[JBS]

Heres my 2 cents---

First, thanks everyone for their imput.I had similar problems with my 23 maxxum outboard.It was very sensitive to trim and changing water conditions.I put a 23 4 blade prop and that helped alot and made the boat track better.I also started adusting the tabs but found I could use the throttle and flaten' her out most of the time unless I was in rough water or hauling a load.I put hydrofoils on my fishing boats and they worked great.I put one on the mate and it did not help very much so I took it off.

 

[jdinvt]

Thats really strange. I have an 87 convincor 251 w/ 454 alpha drive, I have very, very little if any. I can cruse from 35 mph to WOT and you can barely notice./ I have a mirage ss 22 p for prop, and bennett tabs.

 

[bigsbetter]

Thats really strange. I have an 87 convincor 251 w/ 454 alpha drive, I have very, very little if any. I can cruse from 35 mph to WOT and you can barely notice./ I have a mirage ss 22 p for prop, and bennett tabs.

Wow, that's strange. You don't get any porpoise even when you trim the drive at cruiseing speed? I've tried Hydromotives Mirages Tempest Bravo Ones, all seem about the same as far as the porpoise goes, but the Bravo 1 is the fastest and handles as good as any other so that's the one I use. (thankyou ebay).

 

[Mark A]

So, your 454 would have 320 or 330 HP right and my 6.2 should be about the same. I have a Bravo1 drive and fresh water cooling which adds weight and dual batteries. Why does my boat porpoise? Your alpha is lighter and smaller creating less drag. I'll bet your fuel tank is shifted forward from where mine is so the balance of the boat is better.

My 6.2 should perform similar to the 454s that many of those boats came with. From 1986 to 1987 I think Checkmate added a pad that made the 87 a little faster than the 86. What type of top end do you see with the mirage 22?

 

[jdinvt]

my 454 is rated at 320 hp. I also have the duel batt set up. As far as speed goes, I dont have a GPS but the gauge in the boat registered 56-58 mph with a half of tank fuel, me and three of my buddies. I also have a fridge and sink in the cuddy. I took it out again just by myself and it read the same thing. As far as the tank being moved forward more, I dont know. I had replaced half of the floor before I put it in the water for the season and as far as I can remember, I think the distance between the front where it drops into the cuddy and the front edge of the tank it was about 5-7 in of gap between the deop off. Like I said though, dont quote me on that.

 

[ezstriper]

I don't think moving the tank going to feasable, as it goes all the way to the cabin bulkhead, so to go forward means it would be in the step down the cabin....best look other ways...Rob

 

[Mark A]

This information is so useful to me you have no idea! Thank you!

I think I have about twice that amount of space between the tank and the step. (Don't quote me either. I replaced the tank and all of the floor boards about 5 years ago.) I think I have some notes with measurements some place. I will try to locate the notes to see but I should see similar numbers when I get this staightened out which will be a big improvement over what I have now.

 

[Mark A]

I don't think moving the tank going to feasable, as it goes all the way to the cabin bulkhead, so to go forward means it would be in the step down the cabin....best look other ways...Rob

Mine doesn't! That I believe is the problem. Mine has 10 to 12 inches between the step and the front of the tank. The way I replaced my tank and floor boards it should not be difficult for me to play with shifting the tank forward.

Cool information. I really think they would use the position of the tank to balance the boat during trial runs to get the balance correct. I changed weight front and back messing that up.

 

[Craig]

Wow, that's strange. You don't get any porpoise even when you trim the drive at cruiseing speed? I've tried Hydromotives Mirages Tempest Bravo Ones, all seem about the same as far as the porpoise goes, but the Bravo 1 is the fastest and handles as good as any other so that's the one I use. (thankyou ebay).

I can confirm, in the newer models (259/270) anyway, that if you happen to get that perfect prop, the porpoise will be almost a non-issue. When I bought my 270 from the previous owner, he gave me a hydromotive that was way too small, it was labbed finished and "tweeked" to run on that boat with a smaller motor that was replaced before I bought it. It had alomst no porpoise. I sold it though, in my mind it was useless because it ran 5000rpms at 3/4 throttle.

I tried other stock hydros on that boat, and they all bounced badly. Bravo 1's worked the best for me.

-Craig

 

[wca_tim]

I also know that the more weight that I get in the butt end of the boat (ie the newer heavier engine, or when the flotation box was full of a bunch of water and wet foam, mine was had more issues with porpoising... ) the more weight in the back of the boat, the more stern lift it takes for me to run flat and on top the water... ie to balance the boat on it's natural / best angle to plane.

on hydromotive props, you might buy one off ebay and see how it works out. worst case you can probably sell it same way for what you have in it or near. A lot of Fountains come out stock with them on and so there seem to always be some in the local boat shops from people gearing their rigs up. The owner of the shop gthat built my current engine offered to give me one of the ones he had on hand the last time i was out there if they would work right on my set-up. nice fellow. he didn't have any in the right pitch, but i did take the pretty stainless gaffrig spark arrestor...

 

[ezstriper]

thats interesting...mine is a 89 and is all the way forward, maybe moved in later years or is a larger tank...anyway was reading a test on a new fountain 32 this weekend and noticed that they put the batteries in the cabin to help with the ballance of the boat, so there is a idea, not sure i would want to do it but it is possible...Rob

 

[boatn70]

not the same boat but..

my convincor porpoises alot too. the props are the best fix for the money for sure. a hydro q4 was the best for it but i lost 1-2 mph. the rev4 was also an excellent prop on mine. lost no speed and corrected the porpoise.

its my understanding that the checkmates have excellent bowlifting characteristics and when you run at cruise speeds your actually lifting the bow and then falling of the "pad" or sweet spot. it is very annoying. a stern lifting prop is the best route to go, your boat will lift the bow on its own with some trim. my boat runs like an outboard under power with a bravo prop on it.

before you move the tank shift some weight around, have a passenger move about to see if it settles. what will happen though is as you move weight forward it will take more power and more trim to get that bow up, may just move the speed at which it bounces up the scale a little bit. this might work if you dont cruise in that new range.

my advice...keep testing props, you WILL find something that will work well. put together a list of what you want/need to try and post it here.
maybe some board members will loan props for trial. i have before!!

 

[Big Red]

its my understanding that the checkmates have excellent bowlifting characteristics and when you run at cruise speeds your actually lifting the bow and then falling of the "pad" or sweet spot.

That's exactly why a Checkmate porpoises. If you leave the trim down at lower speeds it will stop. Like boatn said the boat is trying to run on top of the water but the driver is being to pig headed with the throttle so the boat falls back down. This is a good thing it does not take a hole lot of power to get a Checkmate out of the water and ride on the pad.

The only real solution to stop the porpoise in a Checkmate is leave the trim down or give it more fuel. And if you start altering parts of the boat to correct it your going to slow it down and mess the ride up.

Checkmate has been building boats since the sixties and I am sure they are well aware of the porpoise problem and have tried different things to correct it. But I feel it probably slowed the boat down so they left things alone.

 

[EightSecV6]

Ive got a 28p 4 blade Bravo on mine and I can eliminate the porpoise at any speed playing with the trim and tabs, pretty much a non issue. My boat is a 1999 259 Convincor.

 

[bigsbetter]

I put a Stingray (old style) on my boat a few years ago to help the porpoising. It definitley helped!, and with no other draw backs that I could feel. A couple weeks ago, I must of hit a log in the river driving home at night and it broke in half. I removed the whole thing, and went out over the weekend camping and boating. I didn't realize how much help that silly thing did for my boat! I hate driving without it on the boat! I will be getting a new one very soon! I've heard bad things about the new Stingray xrIII's (no drilling required)so I'll either get the same old style or maybe try a SE Sport 300....Has anyone had any expierence with both the Se Sport 300 and the Stingray to compare them?

 

[mmhhughes67]

sounds like iam not the only one with this problem.... my 92' convincer does the same thing and i have spoke to Mike combs and he suggested a bravo1, 24 pitch ,4 blade but that gave me to much lift and the boat bow steered like crazy !!! I run my boat trimed all the way in and the tabs set about at 4 and it seems to ride the best. I have been told this was a problem with these convincers in the early 90's because the molds were starting to go away,then the hull changed after that ?? We have many c-mates in my area and its seems everyone has a reason why they do this, but no real solution ?

 

[daren34]

even the smaller stern drives are very sensitive to trim

on the eluder i have now and on the starlet every change in rpm or throttle stetting requires a change in trim

i tried a few props aluminum, stilletto,mach and mirage

i like the mirage for everyday and skiing
it also has the softest ride

the stilletto was horrable.

the aluminum bad holeshot no top end

the mach sterdriver had a ton of sternlift better for wakeboarding
a little slower on top could have run more pitch

bigdave ran my mirage on his sterndrive diplomat and did not like the mirage not enough stern-lift with a v-8 in a 17 ft 8in boat

good luck daren

 

[wca_tim]

so far all three of the stern lifting props that I've tried, including a couple of hydromotives and an alder merc cleaver have run straight and flat with little or no porpoise when trimmed right. The 29 hydromotive was the best so far, but that's just too much prop for me to turn and pull boarders and skiers out of the water with easily (and without putting a huge strain on the drive) and tops out a little over 5000 rpms rather than the 5500 I am shooting for. That's a 15 1/2" 4-bladed prop. I'm looking around for a 4-bladed 14 1/2 inch or thereabouts diameter in 28 or 30 pitch... thinking about trying something like a drag or et style outboard prop, maybe the right merc or mazco cleaver would do the trick... or seeing about having a bravo or hydromotive cut down if what I can come up with over the next few months doesn't give a clear idea of what the best is going to be...

The 27" Mirage plus I've been running isn't the right one for top end, but handles well, hooks up and does fine for pulling skiers and boarders and was cheap and available...