Prop/Motor/Performance issue

tlc954

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Jun 16, 2008
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Recently purchased a 2007 Crestliner 1750 SC Fishhawk from local dealer. 2007 Merc. 115 EFI XL 4-stroke came w/ Merc. Black Max 13.25" x 17" prop. Hull wt. =1100 lbs., Motor wt. = 410 lbs. Total gear wt. = 400 lbs. W/ 2 people in boat (400 lbs.), boat planes very sluggishly. WOT @ 5800 RPM nets 37 mph(gps) but engine not fully trimmed. Trimming full out causes prop to ventilate. Cavitation plate appears to be approx. 1" lower than bottom of hull when motor is trimmed down to where the cav. plate is parrallel to hull bottom. Hard to tell where cav. plate is positioned on plane due to the intense spray between the cav. plate and the secondary lower unit fin. Motor is mounted such that the transom wrap-over bracket of the mount is 25" higher than the bottom of hull. Boat won't plane with 4 people (only additional 220 lbs, ya..they're light gals). Tried these other props w/ 2 people in boat:
Solace Amita 4 blade 17p - Better hole shot - 5400 rpm WOT 38 mph- @80% trim, prop ventilates. Solace Amita 4 blade 19p Hole shot similar to merc. prop - 5200 rpm WOT 39 mph, @80%+trim, prop ventilates. MW Ballistic SST 3 blade 21p - Hole shot sluggish-5800 rpm WOT 39 mph, able to fully trim without ventilation.
The only prop that I think would even come close to being able to plane boat w/ 4 people is the 17"p Amita 4 bladebut hole shot would be sluggish. Dealer ensures me this rig is set up the way I want it. I don't think so. It seems I should be able to prop it, or change motor height on transom to get mid to upper 40 mph out of this rig w/ one prop (2 people), and sacrifice some top end for a hole shot that would just about yank the arms of a skier off with another prop. WOT throttle range for this engine is listed as 5800rpm - 6400 rpm. Anybody got any ideas as to whether or not the engine is mounted @ the proper height, and what I should be looking for in a prop? My experiments are getting expensive.
 
Last edited:

steelespike

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Apr 26, 2002
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19,069
Re: Prop/Motor/Performance issue

Not a pro but it seems to me a 19"pitch stainless will give you about 6,200 rpm.better hole shot and possibly increase speed.If it still gives you trim without venting then you might be able to raise the motor a little.Best height is the highest without venting problems.
Also be sure it pumps water.Most likely one of our experts can supply some details.Perhaps a specific prop suggestion.
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

Thanks for the input, Steelespike. I'm stumped on this one. I've got plenty of experience tricking out the bass boats I've owned in the past, but this is my 1st aluminum semi-v hull. I know its not a pad hull, but my expectations for this rig shouldn't be out of the ordinary. On one hand, if the aluminum props I'm trying are blowing out at nearly 80% trim, that would indicate the motor may be too high on transom and needs to be dropped. On the other hand, because every prop I've tried between 17p and 21p makes a minimal impact on speed, with only a moderate impact to rpms, it would indicate there is a finite reason with the set-up (excessive drag) that is keeping the hull from achieving any more speed, which would indicate the motor needs to be raised. The dealer seems really reluctant to help me out, and if I have to move the motor, I only want to do it once. It was so easy when I had jack plates. Hope the experts in this forum can give me some insight.

TC
 

Randybeall

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May 2, 2008
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319
Re: Prop/Motor/Performance issue

Seems to me we are forgetting scientific method. Change only one variable at a time. The 4 blade information may be misleading because of the different area of prop surface in the water. I would suggest that this combo may not trim fully out, I know this is common in bass boats and some others but this hull is different. Based on the info presented my WAG is to raise the engine till the ventilation plate is even with hull bottom and go back to orignal prop. Trim carefully in small incerments and find the 'sweet spot'.
By the way, 4 girls, 220 pounds, unless they are children, stop spending money on props and buy them a meal!
 

Silvertip

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Sep 22, 2003
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Re: Prop/Motor/Performance issue

Since none of your combinations has allowed revs anywhere near 6400 RPM I would tend to have a close look at the engine to make sure it is tuned properly. The most you've been able to wring out of this combo is 5800 so that still leaves you 600 RPM short of ideal. Thats roughly 3-inches of pitch with prop alone. If the engine checks out ok, then setup is next in the process. Pick the most promising prop of the bunch and play with setup. When that's optimized, you can make final pitch selection but stay with the same prop manufacturer and style. Change prop manufacturers and/or style at this point and you introduce another set of variables. That engine should have no trouble twisting a 19P three blade stainless with lots of cup and still provide good hole shot.
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

Thanks again Randybeall and Silvertip for your input. Randybeall, let me clarify my statement; when 4 people were in the boat and it wouldn't plane, it wasn't 4 girls @ 220 lbs xtra wt., it was an additional 2 people (xtra wt. of 220 lbs.) other than the original listed 2 people @ 400 lbs xtra weight. My wife and my son's fiance are both 110lbs. Point being the weight of those two gals would be on par to putting only one more of my fishing buddies in the boat, in addition to myself and my son. And the boat still wouldn't plane out. I will indeed get the motor positioned on the transom properly, and again test the rig with the 4 props I have. Silvertip, I'm guessing the motor is tuned fine since it only has approx. 3 hrs. of run time on it, it runs smoothly and responds to throttle up immediately. Whenever the props I ran went into ventilation, the motor had no problem reaching that 6400 rpm threshold. Now the question remains, can any of you guys point me in the direction of what type of prop design (not pitch) might work the best on this rig combination for providing optimum top end with 2 people in the boat, and still provide a decent hole shot. i.e. - larger blade area, steep rake, deep cupping, etc. There's got to be thousands of these rigs set up just as mine throughout the good ole' USA.
Thanks everyone for taking the time to respond.
TC
 

MikDee

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Jun 6, 2007
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Re: Prop/Motor/Performance issue

Hey TC, Stop dragging the anchor, and it'll plane! :D j/k

It sounds like you have a nice combo there that should fly!
Is the motor broken in? 3hrs run time and your pushing it?! :eek: It takes about 2 full tanks of gas (12gals) before you should push it any. Everything mechanical is tight inside! The Michigan wheel is probably giving you the best performance because they usually have 1) a bigger diameter 2) more blade area. Give yourself, and that engine a chance to get loose ;) Then much later on that prop might be your best bet, if you drill a couple of ventilation holes in it. There's a special procedure to do this, and it must be done a certain way, also I don't know if it applies to your rig,,, nor do I know the specifics, but there are guys here that do, and can help you down the road, good luck Mike
 

Silvertip

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Sep 22, 2003
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Re: Prop/Motor/Performance issue

Don't get me wrong about the state of tune. Also understand that an engine running on half its cylinders will rev to 6400 RPM with no load on it (as in neutral or ventilating). So even though the engine has only three hours of run time, it may still not be set up properly. As they say -- "stuff happens". And I would also suggest that with only three hours of run time, the engine is not fully broken in and therefore a little shy on top end RPM. I would not make any rash decisions until you have more time on the motor.
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

Thanks again for the insight guys. Mike, what's an anchor?? :) And thanks for the complement on the rig. It should be a sweet ride when I get it working with all your guys' help. Maybe I'm just too picky, and too used to having my cheeks slapping my ears @ WOT with the bass boats I've had in the past.
Just found out my neighbor has a ported 19p Laser II on his Merc. 115 2-stroke that he said I could try after I get the engine raised on the transom. Silvertip, I was wondering about the break-in period myself, and how a tight engine might affect the ability of the rig to perform. I'm pretty confident the engine is tuned, and also know I haven't deviated from the manufacturer's break-in procedure. I'm at the point where I should be able to run this engine @ WOT for 5 minute increments at a time, albeit I haven't had it @ WOT for any longer than possibly 2 minutes. It should be loose enough by now to give me somewhat of an indication as to where I can expect this rig to perform as it is currently set up. I plan on getting the engine raised sometime next week, and I'll run the tests again on all the props. I'll post my results for sure. Quite the learning experience so far.
Thanks again, guys.
TC
 
Joined
Jul 4, 2008
Messages
18
Re: Prop/Motor/Performance issue

If I remember right, that 4 stroke RPM range is 5000 - 6000 @ WOT. Your boat is similar to the one in my signature. Mine started out with a 17p aluminum. Lousy holeshot, and about 40 mph w/GPS. I tred alot of different props (dealer let me try them) and I ended up with a Vengence SS 18p and a backup Black Max 19p. Both props gave a good compromise of holeshot and top end. I ran per GPS 44-45 mph with an occasional 46 @ about 5600 RPM.

I usually fish just by myself so your results will vary.
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

If I remember right, that 4 stroke RPM range is 5000 - 6000 @ WOT. Your boat is similar to the one in my signature. Mine started out with a 17p aluminum. Lousy holeshot, and about 40 mph w/GPS. I tred alot of different props (dealer let me try them) and I ended up with a Vengence SS 18p and a backup Black Max 19p. Both props gave a good compromise of holeshot and top end. I ran per GPS 44-45 mph with an occasional 46 @ about 5600 RPM.

I usually fish just by myself so your results will vary.

Hi Runaway,

Your older Merc. 4 stroke probably was rated in that WOT throttle range. I believe in 'either '05 or '06, Merc. scrapped the Yamaha power heads in their mid-range HP engines for one of their own design, which implements many, but not all of the Verado technological advancements. I can assure you my owners manual calls out a WOT range of 5800 - 6400 RPM on this engine. My rig goes to the dealer Monday for an "engine lift" , and a prop trial. Funny you mentioned the Vengence prop. I just discussed trying that design with Dealer today in an 18 and a 20 pitch. Silvertip, I'm taking your advice to the bank on this one, too. I told the dealer to check that motor out from head to toe, and if there's a timing issue, burn a new eprom :)

TC
 

Silvertip

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Sep 22, 2003
Messages
28,758
Re: Prop/Motor/Performance issue

It isn't only timing -- there are many things that can prevent these new engines from performing. Lazy injectors, laszy sensors, and engine that requires more break-in time since it may be on the tighter side of the manufacturing tolerances to name just a few.
 

K.P.

Seaman Apprentice
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May 29, 2008
Messages
39
Re: Prop/Motor/Performance issue

Sorry to tell you TLC but you will definitely not see upper 40's with that rig. Maybe mid 40's with just you and a light load of fuel but more likely low 40's under normal conditions. Look at the Merc website for performance and rigging info on similar sized rigs. (link below) Raise the motor one or two holes and put a 16 pitch Vengence on it. That should get you where you need to go. A 4 blade is only going to make you go slower and you'd need to drop to a 15 pitch. You definitely want to get that sucker turning near the 6400 RPM max.

http://www.mercurymarine.com/look_d...tle&Section=outboardChecks&fourStroke75115=12
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

Got the rig back from the dealer today. Verified engine was performing as it should, and tach was accurate. They put the boat on the water, and afterwards strongly indicated the motor didn't need to be raised, nor would they feel comfortable doing so because the hull seemed to lift well as is, although they agreed the hole shot was sluggish w/ the original 17" pitch merc. prop they sold me w/ the rig. But they also said they saw 41 mph (gps) @ 5800 rpm w/ 2 people in the boat, which is contradictory to what I initially saw (3 mph slower). But I wasn't there at the time. They ended up swapping the 17" Merc Black Max for a 15" Merc. Black Max @ no charge and said they got 41 mph (gps) @ 6200 rpm w/ 2 people in the boat, with a much better hole shot. They also tried a 16" Vengeance they said ran 42 mph (gps) @ 5700 rpm w/ 2 people in the boat. I took the boat directly to the lake to verify their findings. With myself and my son in the boat, hole shot was much better, might even be able to pull a skier up now. But couldn't get top end to exceed 38 mph (gps) @ 6200 rpm at any trim level, which makes me question the other findings the dealer related. Supposedly, the dealer also consulted Mercury Marine and a design engineer from Crestliner for their input, but said he basically got the head-scratching " I dunno" answer from both of them over the phone, which sounds suspect to me, also. I'm going to get a few of my buddies together over the weekend and have them help me raise that motor one bolt hole, regardless of what the dealer thinks, and then try the props again. If any results are much different, I'll post my findings. Otherwise, it's back to the experimentation stage w/ various prop designs. Thanks everyone for your insight and suggestions. I never figured on getting a masters degree in fluid dynamics and hydro-propulsion out of this ;)
TC
 

MikDee

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Re: Prop/Motor/Performance issue

Good Luck, So, you're on your way to being a hydrodynamic engineer now :D keep us tuned in ;)
 
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Re: Prop/Motor/Performance issue

TLC, How funny is this, I find myself in almost the same situation. Just bought a 2008 crestliner 1650 running a 75hp mercury fourstoke, current prop is a 13x17p prop but am only getting 4900-5000 rpms at wide open throttle. My stealer wants to go down to a 15p prop to raise the rpms, by the way I'm currently only topping out at 32mph. One thing I do notice like u have noticed on your boat possibly, is the fact that my cavitation plate is a full 1" below the hull, the dealer is reluctant to move it up. Wonder why? I wonder if I can run a jack plate on this style of boat?
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

mikesn...

I had my boat back to the dealer this past week. I TOLD them to move it up one hole. Well, they moved it up two holes, but I didn't check it at the dealer because I was more worried about the fact that I trashed out the front u-joint in my pick-up on the way there to pick it up. So that's my own fault for not catching it on the spot. Anyway, when I found it another bolt hole higher, I measured the AV-plate to be 5/16" higher than the hull bottom when parallel to it. So, rather than rag on the dealer, I was waiting to post back any results until I got a chance to try my props out again where the motor is mounted now. I found a friend of a friend who has the same model boat I have except a few years older with a 115 Yami 4 stroke. He's turning a 20" pitch SST prop @ 6000 RPM for 51 mph (gps) with 2 people and a medium load of fuel. He said the hole shot is kind of weak, but it still will get up in really rough water. He said his motor is as high on the transom as the mount will allow. Of course, I emailed him for more specifics, but haven't heard back from him yet. I have several friends that have the 1650's w/ 90 HP 2-strokes and they're turning 19" SST props @ 5400 RPM for low to mid 40 mph (gps) with those rigs. A 75 HP motor may only get you in the mid to upper 30 mph range, which is basically where my rig was running prior to the motor lift. Stay tuned for my findings.
TC
 

tlc954

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Jun 16, 2008
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Re: Prop/Motor/Performance issue

Had a chance to run my rig this weekend with the enigne raised two bolt holes from the original set-up. Tried 3 props, two of which I ran before. The rig performed quite well, albeit I didn't see the increase in top end I was hoping for. The AV plate is now just above the water level when trimmed out on plane. I never starved the engine of water, even in relatively sharp turns. And the hull seemed very solid in the water with all the props I tried again. Here are the results from my trial. All speeds are by gps, 2 people in the boat with a medium load of fuel:

Solas Amita Al. 4 blade 17" pitch - originally ran 38 mph @ 5400 RPM, and would ventilate @ 80% trim.
Now runs 41 mph @ 5800 RPM and ventilates @ about 70% trim. Hole shot good.

Solas Rubex Al. 3 blade 19" pitch - runs 40 mph @ 5600 RPM and ventilates @ 70% trim. Hole shot weak, but still could get on plane.

MW Ballistic SST 21" pitch - originally ran 39 mph @ 5800 RPM and could trim full out without ventilation.
Now runs 41 mph @ 5600 RPM and ventilates near 80% trim. Hole shot similar to Rubex.

Didn't take the time to run the 15" merc. prop the dealer swapped for the original 17" pitch Merc. prop, but I strapped that prop on the rig as soon as I got home and will check it out this week. I suspect I may end up spinning that prop a bit faster than I want right now, but the testing will tell. Also will check the 19" Solas Amita 4 blade for information's sake, but I think that prop will be on the auction block.
The 19" pitch Laser II I was going to try ended up being a 22" pitch, so that prop got strapped right back on the neighbor's rig knowing full well I wasn't going to be able to spin it.
It's looking like the pro's on the forum are correct in that I'm not going to see the upper 40 mph range with this rig as I hoped. But I think if I can find the right prop now, I should be able to get in the mid 40 mph range @ that 6100 - 6200 RPM range I want. KP, that 16" pitch Vengence you mentioned looks like it just may be ticket now. I'd like to think a 17" pitch 3 blade would gain another 2 - 3 mph over the 4 blade if it will spin a couple hundred RPM higher than the 4 blade. I also think the "friend of friend" might just be "f.o.b.s." about his rig's performance :).

Anyway, Thanks so much for all the great feedback and input. I've learned a ton of stuff from you all.

TC

TC
 
Joined
Jul 22, 2008
Messages
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Re: Prop/Motor/Performance issue

TLC, the local dealer put on a 15p prop, now rpm's top out at 5900 solo with the top down and tops out around 35mph.. With the wife and the top up my speed and rpm's are down to 5700 and 32-33 mph respectivly. My local prop shop sugests moving the engine up so the cavitation plate is at least above the bottom of the hull as right now it's a full 1 " below, I would have to buy a new prop though, at the very least go back to a 17p because they say the rpm's would rise. With the current setup I have a lot of pitch problems if I try and trim out very far.
Am currently thinking of the nautitec sx tabs, have been told they would help with the pitch problems. I think the reason I have pitch problems is the fact that the water coming from under the back of the hull is hitting the top of the cavitation plate and get worse when u try and trim out the engine at speed. Everything I've read on the trim tabs sugest even if i did raise the engine the tabs would still be a benefit..:p
 
Joined
Jul 22, 2008
Messages
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Re: Prop/Motor/Performance issue

How funny is that, I just logged on and posted a reply to u'r previous msg, when I checked back u had posted your results..
 
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