New Boat Performance/Propeller Selection Low RPMs

[weaver_je]

I recently purchased a 2006 Regal 1900. The current prop on the boat is a 17 pitch 3 blade. From the owners manual I should be around 4800 RPM's WOT. With trim all the way down and 2 people in the boat I'm only getting 4000 maximum RPM's. If I trim up to just under half way (on the trim gauge) my RPM's go up to just under 4500. So my first question is with a 17 pitch propeller do those numbers seem right? I would think that I should be more around 4500 when trim is down. As a side note I'm only getting about 38 MPH top speed which also seems low (increasing to about 42 when trimmed up slightly). From the specs on the boat it seems I should be closer to 50 MPH.

Since this is a new boat I'm just trying to get a baseline of what I can expect. The boat seems to perform well with only a couple people on board, but when loaded with 7 or 8 people it seems pretty slow getting up on plane. Takes about 20-25 seconds to get up to 20 mph before it starts accelerating quicker. I'm mostly concerned with performance for water sports and want to get the best hole shot I can. Am thinking of switching to a 4 blade prop, but was hoping to verify that the current numbers seemed correct.

Some additional information:
4.3 L 190 HP Volvo GX Engine
Volvo Penta SX drive (1.66 Gear Ratio)
15x17 Aluminum Prop
2006 Regal 1900 (19' 9") 2,800 lbs

Thanks for any information.

 

[rndn]

Re: New Boat Performance/Propeller Selection Low RPMs

First off, Welcome to the iboats.com forum!!

The trim should be lowered all of the way down in order for the boat to climb out of the hole the quickest. As the boat climbs out of the water you should then trim the outdrive up to get the bow out of the water. If you go too far up you will hear and feel the prop venting and losing touch with the water. Trim back down slightly until this stops. You should now be trimmed properly and be able to provide numbers for this forum to help you select a prop.

A 19 foot boat with 7-8 people on it will be a little slow out of the water. If this is a fairly common load for you you will want to look into trim tabs or smart tabs. The tabs will greatly assist getting the boat out of the water with a heavy load, as long as the boat is also propped correctly.

With the boat trimmed out properly, please provide the rpm's and speed at WOT(wide open throttle). As you mentioned water sports, you may also wish to consider a 4 blade prop as it will also help the boat climb out of the water better than a same pitched 3 blade prop.

There are many helpful people on this forum and they will assist you once you give them the information they need.

 

[hwsiii]

Re: New Boat Performance/Propeller Selection Low RPMs

Je, your numbers are good for what you are doing right now, your prop slip is very good. but if you intend on carrying much heavier loads we need more information.
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 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