Loss fo Performance and Efficiency

[BRIAN03]

Re: Loss fo Performance and Efficiency

There is a cavatation issue with the new Yamaha gear case. They have moved the water pick up location on the lower unit. Yamaha has move the pick up lower on the case. Yamaha recommends to file the leading edge of the case. I've tried it doesnt help. I have put T-H transom shim in to help. I think they should have put a low water pick up in like Mercury big case. The lower unit where running out of water on the top end. I bet a another new case will come out with a low water pick up. The new engines have rpm reduction when you run them hot. Thats why they had to address this issue. We have been putting nose cones on these engines for years with low water pick ups.

 

[Laveread]

Re: Loss fo Performance and Efficiency

Did a lot of work on the boat with regards to other little problems but of course I still have the original problem. I took a good look at the lower unit and it's position with the very bottom of the "V" in the hull. The prop actually extends 2 - 3 inches above the lowest portion of the "V" putting the first horizontal (whats it called) fin or stabilzer (in aviation terms) about 5 inches above the lowest portion of the "V". Should this be lower? If it should be then I have major problems because the motor is already as low as it will go.<br /><br />It makes sense to me that if the water flow across the prop is being disturbed by the hull causing a difference in pressure between the top and the bottom of the prop then cavitation will occur. Solution??? A longer shafted lower unit but does Yamaha make a longer shaft for the 4 stroke 225hp? I believe they only make one length right now. Regardless, I am stuck with a poor performing boat which was originally an outstanding performing boat.

 

[Dhadley]

Re: Loss fo Performance and Efficiency

The flat plate right above the prop is commonly referred to as the "cavatation" plate. It's actually an anti-ventalation plate. If the motor is bolted directly to the transom, that plate (when trimmed to parallel) should be no lower than even with the hull and possibly up. How far up depends on your hull type and prop type.<br /><br />However, if the motor is mounted an a bracket that extends the motor further back, the AV plate could be 5" up. IE; if the motor is on a 26" to 28" bracket (26"-28" behind the transom) it would be about right that the AV plate is 5" up. Perhaps more with a 4 blade prop.<br /><br />It still should be turning higher rpms if the prop is losing bite and breaking loose. Not turning less rpms.<br /><br />I would still do the test prop deal. Somehow we have to seperate the boat and motor.<br /><br />Good luck!

 

[Laveread]

Re: Loss fo Performance and Efficiency

I am planning on taking the boat to Pro Sports in Melbourne tomorrow. I am going to leave it with them after explaining everything that is going on. I'll recommend they use a test wheel to check the performance. Hopefully they have one. I am also going to recommend they try different props to reachieve what I have lost.<br /><br />They have some other things they need to do to the boat too so I am sure their home office in Alabama will get wind of this and hopefully figure out they can't just blow me off anymore.<br /><br />Thanks to everyone who has helped me here and have given me a better understanding of the hydro-dynamics of boats and motors. Once this is all settled I will repost the outcome. Depending on Pro Sports action or lack of action will determine my next steps.

 

[Knightgang]

Re: Loss fo Performance and Efficiency

Is this the 2550 BW that is on the Pro Sports website??? If so, here are the specs of the boat:<br /><br />Length 25' 5” <br />Beam 8' 6” <br />Draft 13” <br />Approximate Weight 2760 lbs. <br />Horsepower Capacity 300 HP <br />Fuel Capacity 121 gals. <br />Maximum Capacity 8 persons <br />Deadrise 25° <br />Capacity 1240 lbs <br /><br />Here is a link to the performance data on this boat.<br /> http://www.prosportsboats.com/pdf/2550BW.pdf <br /><br />Looking at the boat, if your set-up is the same, it does not have a transom bracket and the cavitation plate should be no higher than about 1" above the bottom of the keel, it also should not be any more than 1" below the bottom of the keel. I agree with the test wheel, lets see what happens.

 

[Laveread]

Re: Loss fo Performance and Efficiency

Yes, that is the the boat, 2550BW. You are correct in that there is not a bracket but the keel does not extend all the to the back where the motor is mounted on the swim platform. I will have to measure the distance from the end of the keel to the end of the swim platform for exact measurements but if I had to guess I would say that it is appx 20" - 24" behind the end of the keel. Essentially it is a bracket.

 

[Laveread]

Re: Loss fo Performance and Efficiency

Thanks for the link to the performance data. I have not been able to find that data. Looking it over it is very close to the numbers I was able to get before. The difference here is that I have a 4 stroke vice the 2 stroke that was used in the test. Going from averything I have heard the 4 strokes are better economically so my numbers were actually a little better in GPH. <br /><br />Also, the tests show 46.6mph at 5,700rpm with the 2 stroke. I was able to achieve 49mph at 6,000rpm with my 4 stroke.<br /><br />Now I have a some firm evidence to bring to Pro Sports. Hopefully this will keep any arguements to a minimum. Thanks again!!!

 

[Knightgang]

Re: Loss fo Performance and Efficiency

Most of the info that I have seen on two strokes vs Four Strokes in the same make and same horsepower shows that there is only marginal difference. I hope you can use this to support your argument and good luck. <br /><br />BTW, that is a nice looking boat. I hope you can get everything worked out. It looks like a nice chunk of change to end up unhappy and either have it sit, or sell it and cost you more money.<br /><br />I have a feelimg it may come back to the adjustment of the controlls since eveything had to be re-rigged. At least we can hope.<br /><br />Knightgang

 

[v12mac]

Re: Loss fo Performance and Efficiency

Any update? <br />Mac

 

[Laveread]

Re: Loss fo Performance and Efficiency

I delivered the boat to a Pro Sports dealer on Tuesday. We discussed at length the problems that have been noted in this forum and he is very interested in fixing the problem. He has already talked with the owner of the dealership and my old mechanic in Jacksonville. He first has a few other things to take care of on the boat then he will begin the performance problem. He is familiar with that model of boat and motor setup so he is planning on putting the boat in the water and taking it on a run. If he can't get the boat back into the same performance parameters as before then he has already said that himself and the owner of the dealership will make a conference call to Pro Sports for a solution.<br /><br />So, although I still don't know what has happened to the boat I feel better knowing that I have 2 mechanics and the dealership owner on my side. I won't say who the dealership is yet but apparently he has quit ordering boats from Pro Sports. He just isn't happy with them (me too) so in essence he has nothing to lose by being in my corner.<br /><br />I should know something early next week as far as a diagnosis is concerned.

 

[Laveread]

Re: Loss fo Performance and Efficiency

Here is the latest update on my boat with regards to its loss of performance and efficiency.<br /><br />First problem was found to be the trim tabs in the full up position still dragged in the water a little causing a decrease in top end speed and susequently a loss of fuel economy. Fixing this gave me back appx 3 mph. Top end achieved after this fix is now 43mph and the motor is able to re-achieve 6,000rpm. I am still short 5 - 6mph in comparison to the original hull.<br /><br />The mechanic is now working through a myriad of different props trying to get as much of the original 49mph back. The latest test with a larger diameter and shallower pitch gave me two more mph at a lower rpm (5,600). He is going to try one more prop in an attempt to get me 2mph more which will satisfy me for now. If the fuel economy rises back to where it was or come close to that point then I'll be happy and accept the boat back.<br /><br />For your knowledge here is what we have been through in props. Original prop is a Yamaha 14 1/4" x 20 giving 6,000rpm and 43mph. Next prop was a Mercury 14 1/4 x 23 (used prop) giving us 6,000rpm but only 40mph (we couldn't explain that). The next prop was a Stiletto 14 1/4 x 23 giving us 5,600rpm at 43mph. The next tried was a Yamaha Salt Water Series 15 1/4 x 19 giving us 5,500rpm at 45mph, getting close. The next prop to try is a Yamaha Salt Water Series 15 1/4 x 17 which should bring the rpms back up to 6,000 and will hopefully give me 47mph which will be close enough to make me happy in the speed spectrum.<br /><br />The service manager helping me here is very knowledgeable and is determined to make me happy. If you live in the Melbourne, FL area then I recommend him. The dealership is Boathouse Discount Marine.<br /><br />Once I have the results I will post them here.