high altitude suggestion

[powderhombre]

well if you read my other post, you might know I tore up my prop first time out, so I didn't get a chance to really play around with speed and RPM's. the prop was a 151/2 x 15. my friend say's thats a huge prop. so my question for some of you who may have an opinion... the engine is an OMC 3.8 lt. rated at 175HP. the boat operates at 8000 feet above sea level maybe as low as 4000ft east of Denver Co. the only estimate I have is before I messed up the prop I look at my GPS and it said 13 miles an hour and I think I was running around 2500 - 3500 RPM. I know thats not fast, although being a newbie boater it felt fast enough for moving around the lake fishing. so with this info does anyone maybe have some comparisons for me to consider in buying a new prop? any other high altitude boaters out there?

 

[hwsiii]

Re: high altitude suggestion

Hombre, welcome to Iboats prop forum and we will try to help you as much as we can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can, if you would prefer to not go to this much trouble there are other people who will help you.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
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. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
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
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
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
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.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.


H

 

[powderhombre]

Re: high altitude suggestion

sorry I took so long to get back. I'll try to answer the questions with the info I have; boat: 1982 Beachcraft, Oregon. no model info. 17 feet, beam is 86" cathedral style "V", do not know the rise. do not know the weight. I'm guessing about the 1 ton range. the HP is 175. the make of motor is OMC chevy v-6 with 4bbl. carb. OMC 800 stringer out drive rato is 1.77.1 operating range WOT is 4200 -4600 rpm. boat operates at 8000 feet over sealevel. engine is tuned for altitude, butterfly opens all the way. 20 gal. fuel USGS maximun is 5 people or 750 lbs. 900 lbs. with gear total. prop was am alunimum 151/2 X 15 do not know manufacturer. no hydofoil or add ons. boat came with this prop. I do not know if the PO used the boat to ski or fish, I think ski. boat seemed to handle OK, but in prior post I didn't have the forethought to record all data as I did not know I was going to wreck prop first time out. reason for asking is: since I now have to replace prop, I am wondering is I should go with what was on there or if some one (you) think a different prop would be better for overall speed/planing as wife someday would want to ski. thats all I can give you, your opinion is appreciated. thank you.

 

[hwsiii]

Re: high altitude suggestion

Powder, I show you need a muh larger pith prop if you were running at sea level, so I am urious as to what you mean by tuned for altitude. At that high an altitude if the jets have not been hanged then I understand why you had suh a lower pithed prop.


H