raise motor & verify prop?

[jandyf]

I purchased a slightly used 2008 Crestliner Sport Angler 1750 this spring. I'm quite happy with the boat but I'm a little disappointed with the speed. I've been browsing the prop recommendations. I saw a very similar setup that ended up going with a 4 blade prop. Would that benefit me? I've already collected the requested information. Thanks for your time and expertise.

andy

1. Year, make and model of boat
2008 Crestliner Sport Angler 1750
The latest model hasn't changed much so you can see it here.

2. Length, width and base weight of boat, look for boat decal on back of boat
17' 1" length, 89" beam, 1300 lbs dry weight

2a.What is the maximum recommended HP for your boat
125 max hp

3. Number of people and gallons of gas normally on boat
2 adults + 2 kids, 20 gallons

4. What do you use the boat for
fishing

5. Is it a Deep Vee and if so how many degrees of deadrise
deep V, 17 degree

6. Year, make. manufacturer and model of motor
2008 Yamaha 90 hp 4 stroke

7. HP and gear ratio of motor IMPORTANT
90 hp, 2.31

8. Manufacturer?s recommended Wide Open Throttle (WOT) range
5000-6000 rpm

9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
See photos

10. Is it a bass boat or does it have a pad bottom
no

11. Does it have a hydrafoil, dolefin or trim tabs
no

12. Make, model, diameter, pitch and whether SS or aluminum prop
Turning Point Hustler 13x15 AL
Turning Point Hustler 13x17 AL

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for $ 50
RPM ___________ Speed ___________ No. of people ____________ Gas ________
1 person, approx. 4 gallons
15" pitch: rpm 6050 @ 35.5 mph
17" pitch: rpm 5350 @ 35.6 mph

14. Are you at sea level or a higher elevation, give us the elevation in feet
750'

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
I purchased it on consignment from original dealer in April so it should be good. The motor only has 65 hours on it.

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
15" pitch since I purchased the boat. I think that I should raise the motor the last hole and I think the top speeds seems low.

17. Does the prop show any damage that you can see
Small chips and abrasions on the leading edge.

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
I'd like to get more top speed.

19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

15" pitch:
3000 rpm @ 12.4 mph
3500 rpm @ 17.7 mph
4000 rpm @ 21.9 mph
4500 rpm @ 26.2 mph
5000 rpm @ 29.7 mph
5500 rpm @ 32.4 mph
6000 rpm @ 34.8 mph
6050 rpm @ 35.5 mph

17" pitch:
3000 rpm @ 15.1 mph
3500 rpm @ 20.6 mph
4000 rpm @ 25.2 mph
4500 rpm @ 29.1 mph
5000 rpm @ 33.0 mph
5350 rpm @ 35.6 mph

 

[steelespike]

Re: raise motor & verify prop?

Welcome
H hasn't been around but you did a very good job with his form.
I don't have his expertize but I'll try to get you started.
From my little bit a research it appears you are pretty close to the norm
for the weight and type of boat.From your testing the 17 has produced the best speed for a given rpm and could produce the best economy depending on the actual throttle setting to achieve rpm and speed.A 3 mph improvement at the lower speeds is signifigant.If the hole shot is good
I would say the 17 is pretty close to what you want.It does appear a 16 would get you closer to the mid range of your rpm band.If it drops out of the band with your typical load you might need the 16.Its also possible for a good prop shop to remove a little of the cup on the 17.For the cost of a Hustler prop I think I would go for the 16.
If you don't have any venting(cavitation) problems now you might raise the motor a hole see what happens.You could raise it to a point just before venting becomes a problem.Just be sure it pumps water.Some will live with a little venting to get the best height.You might gain some rpm and a little speed.I would raise the motor with the 17 see what you get.Allways do one change at a time.A 4 blade should improve your low end performance but probably reduce your top end.

 

[Silvertip]

Re: raise motor & verify prop?

I take a different view than "Steel". Yamaha says WOT rpm is 5000 - 6000. With the 17P you are seeing 5300 which is getting real close to lugging the engine, especially at those times when you are heavily loaded. That scenario will require lots of throttle to get out of the hole and top end will be very limited. Next, both props provide the same top end speed so that is also evidence that the 17P is taxing the engine. Just because rpm is lower does not guarantee fuel savings. In fact the opposite is generally true. Because you lug the engine, the throttle must be open farther than necessary so more fuel is being consumed to maintain the same speed even though with a 15P prop the engine runs faster. RPM and throttle opening are not related 1:1. Obviously opening the trottle increases rpm, but how much depends on engine loading. A free running engine will burn less fuel than one that is lugging. Now then -- the optimum prop for your boat is one that allows the engine to run at or very near the top end of the rpm band with what YOU consider an average load. Top speed will be whatever that combination provides so there is nothing else you can do to improve that other than playing with setup. You have already proven that an increase in pitch with the idea of increasing speed only works if the engine had been over reving to start with. Yours was not. In fact it was spot on. I just did a slip calculation and it also showed there was more slippage with the 17P than the 15P. Lastly, before you pop for stainless and four blade props be darned sure you do research and do it well (unless you have deep pockets of course). Two props of the same pitch from two different manufacturers may not and generally do not perform identically so when making comparisons, stay within the same manufacturer and style. That is why prop selection is such a crap shoot. There are other characteristics besides #of blades and pitch. Prop design also includes factors such as cupping, rake and blade shape, blade thickness, material, etc.

 

[Dhadley]

Re: raise motor & verify prop?

Your tests also show how "edgey" a 4 stroke can be. You tested 2 props from the same manufacturer and of the same model which is the correct way to get a basic baseline. There should be about 400 rpm difference, give or take. But your test shows a 700 rpm difference.

We'll assume the motor is performing correctly but that's a big assumption. Speaking of assuming, don't assume it's OK because you bought it from a "dealer" 6 months ago.

A deep V boat has a lot of drag associated with their basic hill design. 1300 lbs (dry weight) may be a handfull for a 3 cylinder motor, especially a 4 stroke.

The prop in the pic is a pretty basic, general use prop without a lot of technology built in. Generally speaking the motor is a little on the low side but that type of prop may not like much more height.

4 stroke motors need to be set up at the very top of the rpm range to perform properly. In this case, as with most 4 strokes, that means 6000 rpm with an average load. Yes, that may well mean that you can hit the limiter with a light load - if you wanted to.

 

[junior1113]

Re: raise motor & verify prop?

i like the idea of a boat lifting 4x15"pitch. and going up a hole with the motor. 4 blades are great for under powered boats. the hole shot and fuel ecconomy would improve. and would'nt be supprised if you picked up a couple mph and keeping wot rpm close to 6000.

 

[cloumar]

Re: raise motor & verify prop?

Andy,

I don't have the same setup of rig - but look at this thread - I had an issue myself with what we could call almost underpower boat, some info in there may be useful - but again be careful it is not exactly the same setup.

http://forums.iboats.com/showthread.php?t=351788


MC

 

[jandyf]

Re: raise motor & verify prop?

Thanks for the thoughts guys. I was surprised with the large RPM drop with the 17" pitch. I'd rather not have the motor raised unless I'm confident it won't cause a problem because I'll have to have the dealer do it.

I'm also curious how a Yamaha prop might fare. I see they have an aluminum "Deep V Series" but the lowest pitch is 17".
http://www.yamaha-motor.com/outboard/assets/whatsnew/T50_%20F115_60_130.pdf

 

[hwsiii]

Re: raise motor & verify prop?

Andy, thank you for filling out my form so well. The two props you have on their right now are running the same 5% prop slip at WOT, and that is about as good as it gets. The 15" prop is running right at Maximum WOT RPM of 6,000 and that is excellent as well. In my opinion even if you bought a SS prop you would not gain over 2 MPH increase in speed and it is not worth it, I would stay with what you have at this time and use the 15" pitch prop and keep the 17" as a spare.


H

 

[jandyf]

Re: raise motor & verify prop?

Thanks. What are your thoughts on raising the motor the last hole?

 

[Texasmark]

Re: raise motor & verify prop?

I have a Turning Point Hustler 23P alum prop and ran it against a high performance SS of 24P on a light boat running a 2 cy 90 3 cyl Merc, 2.3 gearbox.

All conditions the same. The alum Hustler dropped my WOT rpms from 5600 to 5000 and top speed from 50 down to something like 45 (don't remember exactly, been several years).

Dropping pitch you would expect a reduction is mph for a given set of circumstances, but you would also expect the rpm's to rise.

Not a prop expert,but what this tells me is that the alum prop efficiency totally sucked as compared to the HP SS.

So why did I do the test at all? Well my HP SS is heavy and at idle in F gear I get a lot of clutch dog rattle which is annoying. The 3 cyl engine doesn't help matters....probably wouldn't have the problem with the 6 cyl Tower of Power 90. So I figured if I got a light prop it would quit. Prior to this prop I had run shallower pitched SS props with less blade area and didn't have the rattle. The 23P Hustler was the highest pitch alum I could find to fit my Merc....as it turned out even the 23 was too much.

Well the Hustler is back in the box after only one run and the SS is back on. To prevent the rattle, I do a lot of F-N shifting when loading on the trailer. A bit of a hassle but I'll take the performance any day.

Now in all truthfulness, if you are a low speed guy and spend a lot of time up and down, or right at planing speed, the Hustler is a good choice and outperformed the SS......course that's not what the SS was designed for. Grin

HTH

Mark

 

[hwsiii]

Re: raise motor & verify prop?

Andy, if it was me I would raise it up one notch.


H