Hwsiii

[fourwinnsnate]

I have just been doing some research and i've found out that my motor actually puts out 300hp im just thinking this may change the prop that i will want to buy
When i bought the boat the previous owner said it had 255 but as i've been researching everything that i can see suggests it puts out 300 Unless there is anyone out there who knows better it is an OMC Cobra 5.7 GLi volvo penta sx drive
Thanks

 

[hwsiii]

Re: Hwsiii

Nate, it doesn't really matter how many horsepower you have, your boat and motor will NOT even turn a 23" prop to maximum WOT RPM, that is all we need to know, unless you have a motor problem, and that would need to be fixed.

. What used to Be 48mph at 4200-4300 at WOT has now become 48Mph 4000-4100 at WOT
The motor seems to run fine but i did notice with the 23 only it bogs a little when you go for more speed and it doesnt do this with my 21 or my 19
The engine may need a tune up but frankly judging by how smooth it runs, how it fires up first crank every time i believe this is just too much prop for the boat....
There is an advantage to this prop though...i can do 32mph at 3000rpm which makes fuel consumpion very good when doing a lot of cruising

You can use any prop you want to, but you are not going to get 55 MPH out of this setup, SORRY. I know you want 55 MPH, but the only people who can make that happen are the ones who sold you the boat, telling you it would do 55 MPH. Make them prove it to you, they are the ones who said it. And I haven't seen anything to show me that motor is producing 300 HP, can you show me that data. At WOT RPM your motor should be turning about 4,800 RPM.


H

 

[fourwinnsnate]

Re: Hwsiii

so i mean as far as im concerned 46mph is fast enough for me it just doesnt seem to makes sense when boats very similiar with 6cyls can do 50+mph but i guess they can get more RPM outta their motors and they definitely dont have the torque to pull skiiers up. My only concern is that there is something wrong with my motor but i do have a very deep V i wish i could find someone with the same boat/motor combo and find out how theirs does anyways im gunna wait till spring to order the new prop cuz there is no reason wasting money for it to sit on my boat on shore all winter

 

[hwsiii]

Re: Hwsiii

Nate, this is the information I found for your motor.

Alright so here is my dilemma my boat came with a 19P a 21P and a stainless 23P My boat is a very wide and deep 18.5 Fourwinns horizon with a volvo penta 5.7gli which i belive is about 255hp (2400lbs dry weight i believe) With the 19 i can plain at a reasonable speed (about 19mph) and my top speed is about 42mph but i hit rev limiter (4800rpm) at about 3/4 throttle no matter how many people i have in the boat.
Then the 21P will just touch rev limiter at WOT if there are two ppl in the boat at between 45 and 47mph but i can only plain pulling a wakeboarder at about 23mph which is quick when you are being pulled and it just feels wrong.
Then the stainless 23P must have only been used for cruising because i can only get about 4300rpm out of it at 48mph by myself but do 35mph at about 3500rpm no matter how many people in the boat but again only plain at about 23mph.

You are not comparing apples to apples, which is what most people that come here do, that is normal. There can be potential major differences between the same hulls even in the same make and model of boat from a particular builder. A lot of people also come here and try to compare the prop pitch on their particular motor with someone else's and say WHY are they NOT able to use the higher pitch prop that Joe Blow is using on the same exact boat and the same HP motor, and what they are NOT taking into account is the difference in the lower gear ratio in their motor compared to the lower gear ratio in Joe Blows motor. And that is why I need people to fill out my form so I have all the available information I need to help them.

Here is the Boat Test Report for your boat, except you have 255 HP instead of 225, and the test results, and you appear to be running about 48 MPH which is to be expected with the extra 30 HP. And I will tell you these test are usually optimistic, because they do not have any of the normal excess gear most people carry like ice, food, drinks, USG equipment and all of the other paraphernalia we usually carry on our boats. And if I remember correctly you are not running at sea level which also reduces your available HP.

Boat Test Report

The RPM a particular motor turns is the deciding factor if a particular prop will work within the recommended manufacturers WOT range on any particular motor, assuming you are using the correct blade geometry for that boat.
Finding a better prop for a boat is directly proportional to meeting the manufacturers recommended WOT RPM, in almost all cases. That is the FIRST guideline for finding a better prop, then you have to find the prop that is a better fit for the correct blade geometry needed to get maximum performance for your particular uses and needs with your boat, that is the BLACK ART part of finding a better prop for your boat.


I believe this justifies my previous statements 100%, but it has certainly been a long haul to get here. I hope this helps you have a better understanding of what is required to prop a boat for better performance for your intended uses, and maybe you will be able to help other people in the future.



H