Best Prop for Boat & Motor?

[Stevum]

Hello to all,
I just purchased a new (for me) 1987 Lund 4.9 (16') Tyee with a 88 hp Evinrude V4 motor. It has a 14x19 prop on it now & the boat is really a dog out of the hole. Once it's up on plane it cruises at approx 32 mph (I don't know how accurate the speedo is, it seems closer to 40 mph by experience) at 4200 rpm. I was wondering if anyone could give me some advice on a good prop ratio for this boat. I'm not concerned about ultimate speed, just good performance & fuel economy. I should also state that the clearance on the 14" prop is scary. There is a mark on the steering trim tab plate where is has rubbed during operation. I thank everyone in advance for their help!!

 

[Randybeall]

Re: Best Prop for Boat & Motor?

Good question. First go back to the prop questions and topics page and read the read this first sticky. It gives you the list of information which will help make the right answer to your question possible. It would sound like you need a 17 or 15 inch prop but give us all the information and we will give you what you want.

 

[countvlad]

Re: Best Prop for Boat & Motor?

Hello to all,
I just purchased a new (for me) 1987 Lund 4.9 (16') Tyee with a 88 hp Evinrude V4 motor. It has a 14x19 prop on it now & the boat is really a dog out of the hole. Once it's up on plane it cruises at approx 32 mph (I don't know how accurate the speedo is, it seems closer to 40 mph by experience) at 4200 rpm. I was wondering if anyone could give me some advice on a good prop ratio for this boat. I'm not concerned about ultimate speed, just good performance & fuel economy. I should also state that the clearance on the 14" prop is scary. There is a mark on the steering trim tab plate where is has rubbed during operation. I thank everyone in advance for their help!!

speedo not very accurate... GPS or radar ideal.... i believe 4200 is low, im not sure but your probably looking at around 5500 wot for that motor .. what year is the motor??? we can't give you ay good advice unless we know for sure that your tach is working correctly....

try this first http://forums.iboats.com/showthread.php?t=190636

my experience 19 is awfull high for that motor and boat and you might be turning 4200 rpms and WOT.. if thats the case i think you might wanna start with a 15 and go from there....

good luck

 

[Stevum]

Re: Best Prop for Boat & Motor?

Sorry Guys,
I thought I had posted all the required info. I'm not sure on the exact weight of the 4.9 Tyee & the times I've had it out I have only had 3 average sized adults in the boat with minimal gear & no full livewell. The boat & motor are both 1987 models. The Mph & tachometer readings I listed earlier were at WOT. At this time I don't have any means to check the Speedo but as I stated earlier the 30 mph reading seems low. As far as the Tach, the motor is not wound out at the 4200 reading by any means. Like I mentioned earlier I'm just looking for a decent hole shot, cruising speed & decent fuel economy.
Thanks again!

 

[hwsiii]

Re: Best Prop for Boat & Motor?

Were their three people in the boat when got the WOT RPM and speed at 32.

H

 

[Stevum]

Re: Best Prop for Boat & Motor?

Yes, there were.

 

[junior1113]

Re: Best Prop for Boat & Motor?

i would work any set up ussues before buying a prop. where is cavitation plate in relation to bottom of boat. can you post a pic of this?

did you do a compresiont test?

did you check tach accuracy?

i think a 19 should be fine on this setup with little cargo.

may bee a 17 with a load.


wot would be best at 5600-5800. with todays gas.

 

[Stevum]

Re: Best Prop for Boat & Motor?

Junior,
I will look into the relationship of the cavitation plate to the bottom of the boat when I get home. It sure seems like a huge difference in my 4200 rpm to the recommended 5000 - 5500. Isn't the 5800 a tad too high? It sure would be nice if a guy could try a couple of different props before he had to commit to a purchase!! I haven't done a compression check but I could see how that would be in order & at this time I don't have a way to confirm the tach reading. Thanks again!

 

[hwsiii]

Re: Best Prop for Boat & Motor?

Steve, in one of your posts it says The Mph & tachometer readings I listed earlier were at WOT.
At this time I don't have any means to check the Speedo but as I stated earlier the 30 mph reading seems low. As far as the Tach, the motor is not wound out at the 4200 reading by any means.
In another post
It has a 14x19 prop on it now & the boat is really a dog out of the hole. Once it's up on plane it cruises at approx 32 mph (I don't know how accurate the speedo is, it seems closer to 40 mph by experience) at 4200 rpm.
They appear to be conflicting statements.

H

 

[Stevum]

Re: Best Prop for Boat & Motor?

What I'm saying is that at WOT @ 4200 rpm the motor didn't seem to be wound out. (over revved) I also checked the measurment from the bottom of the center of the boat to the cavitation plate & the plate is 1/2" lower than the bottom of the boat in full downward trim. Another thing that I overlooked was that the motor is equipped with a hydroil foil. (Whale Tail) This should help it get out of the hole , No? And yes, the whale tail was on the boat when I drove it previously.

 

[hwsiii]

Re: Best Prop for Boat & Motor?

Steve, like Paul was talking about earlier, you need to move the motor up an 1 1/2" to start with and I will run some numbers for you but i needmore information
We will try to help you as much as we can, but there is certain information that is needed in order to help you. The following form has all of the information that is needed to help you with your problems in finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planing hull boat that needs this information, and most other people who are trying to help you will need the same information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the exact prop you need for your particular uses, and this information is required to do that.
It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed and RPM.

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
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
8. Manufacturer?s recommended 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 or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from prop, how much gas and how many people in boat for test data

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