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Post by acdaddy0 on Sept 25, 2014 15:55:56 GMT -6
Yeh, I concur! I thought my motor was too high causing high tilt blowout when it may be too low. Looking forward to your results as well!
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Post by native77 on Sept 25, 2014 16:31:29 GMT -6
Southern cross
my target height for the cav plate is adjusted to the wake so it acts like a ski. Any higher is for performance guys IMO.
Just talked to a buddy who tricks out mercs, he suggests a 22 pitch based on current rpm and conditions as the prop to try, I have a 14x21 cupped been laying in garage for years. Will give it a whirl maybe tomorrow after I get height right. Theoretical speed increase almost 25%. Would be sweet to cruise close to 30 mph burning a few (3 -4 ish) gallons an hour.
It's amazing this boat is 10 years old and previous owners never got it set up right. Bought the boat right so I don't mind putting a few$ and time n effort into getting it right.
The other boat has a 03 2 stroke 150 Johnson paid just over $5k late 04 from dusky in ft lauderdale. . At the time the 150 2 stroke vs 4 stroke was like $7k difference and the fichts were blowing up all over the place. $7k buys a lot of fuel. It's an 87 20' Morgan built in naples fl. Their no longer in business but they built a hell of a Seaworthy boat. Not fast, not the prettiest but tough and handles seas well. That said its a 45 mph boat at WOT maybe more on a cool day with dense air. Cruises about 30 @ 4000, good enough for me. Lots of local folklore re Morgan. Great rep in the SW Fl and keys
I just just love being next to the guys who spent 30-40k+ for their rig and I got less than 10 in mine doing the same thing they are. I even get more compliments about her than most other boats get. She's unique for sure.
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Post by native77 on Sept 25, 2014 16:33:11 GMT -6
BTW I love ac/DC reminds me of HS.
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Post by acdaddy0 on Sept 25, 2014 17:09:46 GMT -6
Yep, reminded me of cruising in my camaro back in the day!
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Post by acdaddy0 on Sept 25, 2014 17:17:34 GMT -6
Btw, was just out cruising the kids and wife, my plate is under the water . 38 mph at 5400 rpm wot with two girls and wife 30 gallons fuel. Maybe I can do better!??
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Post by T-Topless on Sept 26, 2014 8:30:59 GMT -6
Good luck , but don't think 90hp will turn a 22 pitch prop on this hull. What prop do you have now? 17p? I would guess you could go with 19p max IMO. I have spent a lot of time on props with this hull.
My max speed was with a 24p chopper, but it cavitates terribly (good for top speed only).
FYI - I'm running a 23p Mirage.
Video:
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Post by native77 on Sept 26, 2014 14:58:37 GMT -6
T-topless it's a 17p, max rpm is 6100, suzuki says max rpm WOT is 5500, so I need to trim off 600 rpm. So if we apply the rule of 150-200 rpm change for every inch in pitch that says I can increase pitch by about 3-4 inches lowering RPM by 450-800. These engines have a low gear ratio, 2.59:1, I am leaning towards this having an influence on the pitch to rpm variable. Only way to know is to test it. 3-4" in pitch is about 5-7 mph theoretical increase. That gain plus the engine height gains would be a 10 mph +,- increase from the original setup. Gave it whirl today with the engine height raised about 4" from first post still with 17p prop about 5.5" from when I drug her home. By setting the engine back 4" on the bracket engine will need to go even higher, see pic Much better performance, jumps right up on plane, stays on plane at much lower speed 16 vs20 mph, at 4200 picked up 2 mph, WOT added 3 mph. Cav still not on top of the water stream but can now see the cavitation plate aft of the engine is skiing, meaning there is air above the cav plate at the rear. It's a noticeable improvement, wife (not a gear head) commented it feels faster and rides higher. She's right, it now is starting to feel right, not so much drag and hard trim to keep the bow down. trying to get a vid here. Never did this before, mostly lurked on forums, never posted. Idky my iPhone saved it as mov thought it would be fly. So may not show on some devices.
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Post by native77 on Sept 26, 2014 15:02:44 GMT -6
T-topless, I always wanted a fold down t-top for my other boat, if I am able to get dimensions for the console can you guys do one? I am guessing you work for them, know them or own the business?
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Post by native77 on Sept 26, 2014 15:16:16 GMT -6
Ac daddy, did you ever do a prop slip calculation? That will tell you your theoretical speed, if you can get slip 10% or lower through adjusting prop and engine height you might be able to do better! I do know that too low = drag = lower speed and efficiency!
essentially getting the engine high enough = less wasted power to overcome the drag created by the extra resistance, too high the prop will ventilate and blow out in turns and heavier conditions.
It's not exact science, but if your overreving or underreving at WOT then prop pitch adjustment will help you dial it in. Over pitched I think produces more slip, engine too high creates more air at the prop and more slip. Lots of myths and facts on the interwebs about dialing in a prop.
Your mileage may vary.
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Post by acdaddy0 on Sept 26, 2014 18:34:36 GMT -6
Gonna look into it! I've always just changed it a bit and thought this was except able . Don't know allot about fine tuning as you are doing.
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Post by native77 on Oct 1, 2014 13:14:08 GMT -6
Southern cross
I did research the mechanical and electrical differences.
As as best I can tell the parts, software differences are camshafts and control module. (Look for a blown parts motor in the future perhaps).
im not really looking for the added horses (yet?), just looking to get this dialed in.
By by toying with engine height I gained a few mph at cruising speed and really improved other performance aspects. I am in the process of prop evaluations, cheaply if that's possible. I am gathering up some used aluminum props ebay cheap. Once I have determined the style and pitch I'll hunt for a SS prop. It's kinda like starting fresh as the current 17" pitch prop I feel is under propped by 3-5 inches.
The OE props are all like fan blades with big wide blades, I am tempted to stick a raker style prop just to see if I can spin a much higher pitch than 17. I've never dealt with a 4 stroke or something with a low gear as these have, so it's a bit of an educated guess. I get the sense when I talk to the prop pros, they're guessing too.
i am thinking these few mods (height and prop) will net 25% - 33% increase in performance from where she was when I drug her home. So $115 for a bracket and ?? For the final prop, I'll resell the ones that don't work. So maybe $300 in parts final total.
I used to toy around with drag/street cars in my younger years, HP means a lot , but tuning and tweaking is equally important. Same applies here in my opinion.
To get a 25-33% performance increase for less than $300 ....a good deal in my book.
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Post by native77 on Oct 1, 2014 17:46:02 GMT -6
Prop gods unfortunately is on the other side of the state, they don't travel this far. They do seem to know their stuff. I checked out their forum, they have it locked for new posts so I was not able to ask them directly. I may call them after my first round of tests, I'll know more then. I found a few prop selectors online including the mercury site. The selectors pick 22-23 pitch and a raked prop as an option. I have an "instock" (layin around the garage for 10 years) 21 raker style with med cupped edges, If the selectors are correct this should be close.
Prop gods forum did have a thread of a similar weight hull and same series df90 the final recommendation was 22-23 pitch.
if 22-23 works, this 30 mph wfo setup when I got it becomes 40+ boating2
Not fast but fast enough especially with the GPH at cruising speed. I am used to the 2 stroke 30-40 gallons for the average trip.
As as soon as I get some trials in, I'll post results.
The camshafts for ohv motors don't seem too intimidating, but it looks like the power head has to come off to do it. So not likely ill do that soon. Hell I saw the local suzuki dealer her and in key largo selling brandy new df90a for high 6k and the 115 for just a tad more,Maybe I'll offer this for sale on craigslist and trade up.
Back to reality, I'll just dial this in.....
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Post by T-Topless on Oct 2, 2014 5:15:09 GMT -6
T-topless, I always wanted a fold down t-top for my other boat, if I am able to get dimensions for the console can you guys do one? I am guessing you work for them, know them or own the business? Yes, I am the owner of RNR-Marine. I designed and am still in the patent process for the T-Topless ( T-Topless.com)... What boat do you have? Here are the dimensions we need: > Windshield grab rail width: (Center to Center): inches* (Skinny T-Topless=23-27", Narrow T-Topless=27-31", Medium T-Topless=31-35", Montauk-T-Topless=31-35", Wide T-Topless=35-39", Shadow=27-37", Montauk-Shadow=31-35") > Height from Floor to Top of Grab Rails: inches* > Rear Leg Mount Height (Railing) from Floor: inches* (farthest/lowest point back on rails, or top of console at rear if you have no rear grab rails) > Diameter of Stainless Steel Rails: 7/8" ,1.00" or1-1/4" inches* (No Aluminum Rails) > Cooler Height (front cooler or bait well from floor) = inches (Igloo is typically 19.5")
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Post by acdaddy0 on Oct 4, 2014 8:42:22 GMT -6
Ac daddy, did you ever do a prop slip calculation? That will tell you your theoretical speed, if you can get slip 10% or lower through adjusting prop and engine height you might be able to do better! I do know that too low = drag = lower speed and efficiency! Just did one, 12% slip with aluminum prop! gonna play with motor height then probably a cupped high rake stainless prop in future.
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Post by native77 on Oct 8, 2014 10:12:44 GMT -6
Update: So here are the latest and likely final numbers. 38mph @ 5200 WOT cruising @4000 30mph. Conditions were less than ideal, 10knot wind medium,light chop. So 40 may be possible to the best performance .
No videos, it's kinda spooky tryin to walk around this small boat at nearly 40mph in chop.
Quick review, starting point was 30 mph @ 6100 rpm, 17" stock omc/brp prop. And would porpoise easy, then trim it down and it would stick the bow hard. Engine was too low.
Raised engine, gained 3mph WOT.
Re propped to gain another 6mph.
Raised motor about 4" and bought a fixed bracket, $115 + $40~ in hardware and 5200 = $155
Had a SS 21" raker style prop layin around my garage, from an old neighbor free
Rehub, clean up prop, $60
Summary, $215 increased performance about 30%. Not sure if the efficiency will be the same, likely less than 30% increase.
I hope this thread can help someone dial in theirs, any one running this combination would likely benefit from running 20-22 inch pitch.
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Post by native77 on Oct 8, 2014 10:28:24 GMT -6
Btw slip is about 2-3%, I have never been able to get slip that low, maybe due to the low gear ratio and large prop dia and pitch gets more traction,grip.
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Post by freezerfiller on Oct 9, 2014 14:15:48 GMT -6
Yeah, a lower gear ratio and a larger prop means less slip.. and much better hole shot! SC, I think yours is a 2.38 ratio, so somewhat less than Natives 2.59 so you probably won't go quite as far as he did to reach optimum. BTW Native, that's great you were able to improve the boats performance that much, just by trying. Thanks for sharing your results.
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Post by native77 on Oct 9, 2014 21:07:14 GMT -6
Wow Native! that is pretty impressive performance numbers you are getting out of a 90 HP engine on that boat. My OEM prop is same as yours except is 19 pitch. If I can go to a Raker style and add more pitch, wonder if I can get that performance number up grade. BTW what style merc prop would you suggest is closest to your Raker style. Would that be Laser or Laser II, tempest?? BTW do you know of hand what the rake difference between old prop and new prop are.? Oh I think you answered with regard to a video but were you able to get a glance of your A/V plate and where it was running after raising the engine. Recalled you were aiming to get it to the surface and not necessarily above. Understand raker styles let you break the surface a bit without ventilating. Southern the enerita looks similar, hard to say from just a pic at the merc site. The laser ii looks like a wider blade. Couldn't find a laser I pic. i am not an expert as I rarely do this kinda stuff, but I read a lot and really try to understand a problem before I try to solve it. A problem well defined is half solved I tried to identify the model of this prop, the prop shop kinda just looked baffled and we both settled on "raker" style. This prop is old old old. Been worked before I can see evidence of welds and grinding where the blades meet the hub. i don't know the rake angle of either prop, I can try to post a pic maybe tomorrow, it's dark out now. The best way I can describe is comparing the blade width is about 3/4 of an inch narrower than the OE prop. i will add that the hole shot has suffered but not where I would say its a performance problem, it's just a trade off. Those wide OEM blades seem to really get a lot of low speed grip and thrust. I never see using this for tubing or skiing, if I do I got the old prop which has a great hole shot. i did not get to look at the cavitation plate, it was close to where I wanted it on the last test run. Was pretty choppy on this trial and at that speed a bit spooky to try to get back to the transom. No reason to keep tuning at 2-3% slip. I was trimming motor slowly up and down to record top speed, trimming up past top speed I could feel it ventilate so I know I'm close to best height. It was choppy and it never blew out just the slight ventilation as I trimmed just past top speed this also is where it would just begin to porpoise some. I think it's where it needs to be regarding engine height. Your milage may vary, I don't want to advocate spending $ on a new prop, I happened to get lucky that I had this prop layin around. If I was to keep seeking perfection I would probably drop an inch of pitch and look for a blade style between the raker and OE style to get a few more rpm and regain some of the hole shot performance. Tempest might be a balance between the 2. I got lucky this prop ran good as I had a few aluminum used props in a ebay watch list and 2 lowball offers accepted, but I never made the purchase till I ran this prop. So,,,I'm happy with the results, never thought this thread would go this far. Perhaps more folks should post their hull/engine/prop set ups so others can more easily dial theirs in. Better yet dealers should do it before they sell the darn boats, yeah right..... I do really like the boat for the intended purpose. Next project, move the battery to the right console and a fresh water tank and shower to the left console. Waiting till the marine flea markets to start in s fl to do it cheap ....so maybe another $200~ for those 2 projects, oh and an anchor cleat, WTH. Why did seapro not install an anchor cleat? And what's with a removable nav light? There's a molded spot in the bow for a nav light, so anchor cleat...got one, bow skene chocks maybe $20, and LED nav light 30$? glad to see some nice folks on this board, I'll keep coming back.....
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Post by native77 on Oct 9, 2014 21:11:16 GMT -6
Yeah, a lower gear ratio and a larger prop means less slip.. and much better hole shot! SC, I think yours is a 2.38 ratio, so somewhat less than Natives 2.59 so you probably won't go quite as far as he did to reach optimum. BTW Native, that's great you were able to improve the boats performance that much, just by trying. Thanks for sharing your results. I think at some point the df140 did start using the 2.59 lower unit gear ratio, might want to check into that, it does effect slip calcs and final output shaft speed.
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Post by native77 on Oct 10, 2014 6:18:47 GMT -6
Prop pics for SC. I'm not suggesting this is the correct type style of prop, it's what I had with a close pitch to what I thought it needed.
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