We just recently purchased an older...

[rickyhill16]

We just recently purchased an older Sea Ray boat.  It is a 1987 Seville 19 Bow rider. It has the Mercruiser 175 Alpha I/O motor. I understand that the factory specs indicate the boat should top out around 45 to 48 mph.  Right now best is 37mph.

The dealer did a compression test on the motor before selling it and it is within specs.  Other than this is an older boat, what should I check in order to get the speed up to factory specs?

Ricky Hill

[Mikeeh]

Top speed has many variables that effect it. First, what RPMs are you turning at WOT? That can help tell if you are running the right prop. Is the boat trimmed correctly? What is the total weight of the crew, fuel and gear when you ran it and checked the speed? Are you looking at the Speedo gauge on the boat (very unreliable) or GPS speed? I know that's a lot to consider but I'd start by making sure I was using an accurate speed measurement (GPS) and then check that the RPMs at WOT are within spec.

[Captain_Zero]

Ditto to above. A compression test only shows that it has compression. It's everything else that makes it go fast....need lot more info

[lyleski]

Propeller specs can also make a difference. Back in the day on my dad's Glastron in order to pull out two big slalom skiers we put on a different prop. That took away from the top end speed.

[rickyhill16]

Thank you for the feedback. It is helpful. When I noticed the speed I was using the boats speedometer and not GPS. I will check the GPS next time we take it out. As for the weight, the tank was about half full, two passengers and minimal gear. The trim was adjusted and according to the speedometer it helped and we gained a few more mph,37 tops. I am not sure about the prop, it is a three blade and has a couple of really small nicks. I did not note the WOT RPMs but will do so next trip.

There were a couple of things the dealer fixed before we took delivery, new battery, new distributor, tune up. They also changed a cutout (?) switch, that is connected to the throttle. I just recently changed the oil and gear oil in the stern drive.
I have a kit to replace the impeller later on.

[Mikeeh]

You're on the right track. As to the prop, a couple of nicks won't make a big difference in speed. What you want to determine is if the prop has the best pitch for your boat. Also, stainless steel versus aluminum can make a difference. If you find you still aren't satisfied once you've checked GPS speed I would suggest you take your findings (RPMs at WOT, prop size and pitch, engine and outdrive specs ) to a good prop shop.and see what they advise. Some shops will even loan you props to try out on your boat. Good luck.

[Dino_240sd]

how about the spark plugs, when was last time they were changed? bad plugs will deff drop top end.

[----]

Find out if you have the correct prop to attain that speed.

I have three props for different needs. My 5 blade is noticibly slower.

Interesting with new boaters, speed is everything. Who needs speed. You don't when pulling people, you're on the lake for "fun"