Why is this boat so slow?

[TexasLXC275]

Just bought a 1997 LXC 275 cruiser with a 7.4 EFI and bravo one. At WOT, this things tops out at about 15mph with just one person on it. It doesn't even plane out fully, close but not all the way down. RPM's are at 3100. Engine sounds great. Everything looks and sounds great but I'm just not getting the speed. I know I've got some issues with growth on the hull but I wouldn't think it would slow it down more than 10% of max speed. Any ideas as to what I should attack first.....besides the previous owner???

[Morgan's Cloud]

Welcome aboard ! (I don't often get to say that first)
Yes , your RPM's are way down .. I suspect you should attain at least 44-4600 , not sure of that engine though ..
Try the bottom first.... You would be amazed how much speed you loose with just an eigth of an inch of growth !
After that test again , make sure the engine is tuned up etc. If it still is way down suspect the prop is too large .
Did you do a test run before you purchased , if you did how did it run then ?
Good luck
Steve

[olredalert]

--------Clean the bottom and get back to us........Bill S

[TexasLXC275]

No, didn't do a test run cause I bought it on ebay. Knew I was taking a chance on things like this happening but I low-balled my bid to compensate for this. Guy ended up lowering the reserve to match my bid. Everything else on the boat works great. Better than expected so don't think I've been burned just yet. I had a chance to see the bottom before it was put in the lake. There is about a half inch of crud on it. I managed to blow off what I could at the car wash. Was only able to get to about half the hull cause it was on a trailer. Do you really think that crud on the bottom could cause this?

[Islander]

There is about a half inch of crud on it. I managed to blow off what I could at the car wash. Was only able to get to about half the hull cause it was on a trailer. Do you really think that crud on the bottom could cause this?

Yes.

[ospreyproduction]

YEP! You may also be running the wrong pitch prop too. Doesn't sound like too much to get worried about right now.

[TexasLXC275]

Osprey - First of all, great pic. Second, what prop should I be running on this boat?

[boldts]

We'd need to know what pitch prop is on the boat now. You can figure about 200 rpm for every 1" less of prop pitch. In other words, lets say you have a 23" pitch prop turning 3100 rpms, a 22"pitch prop should bring the rpms up to around 33 or 3400 rpms. A 21" should bring the rpms up to 35 or 3600 rpms and so forth. To only be turning 3100 with a 454 even on a cruiser Donzi is way over proped in my opinion. It reads like they've got a 29" or 30" pitch prop on your boat. Maybe they were never wanting to get the boat on plane? Manatee zones in FL? 15mph is ridiculas for that boat, but hull growth will effect the boat speed, but shouldn't have anything to do with the engine rpms unless like mentioned, the growth is on the prop also? Good luck with the boat and welcome to the Registry.

[mrfixxall]

[QUOTE=TexasLXC275]Just bought a 1997 LXC 275 cruiser with a 7.4 EFI and bravo one. At WOT, this things tops out at about 15mph with just one person on it. It doesn't even plane out fully, close but not all the way down. RPM's are at 3100. Engine sounds great. Everything looks and sounds great but I'm just not getting the speed. I know I've got some issues with growth on the hull but I wouldn't think it would slow it down more than 10% of max speed. Any ideas as to what I should attack first.....besides the previous owner???[/QUOTE

check your prop,their should be a 16x19 mirage on it..

[harbormaster]

The crud on the boat bottom is probably all of your problem.

Go to your local baot yard. Most of them in our area will haul your boat and powerwash the hull real quick for about 100.00.

[oldandtired]

3100 rpm seems normal to me if the boat never even got on plane. It's probably going to 3100 and just staying there. My boat only goes to 3100-3200 rpm coming up out of the hole and winds up right around 5000 at top end. Also, make sure that your bilge is dry and that there is no water in the boat. It sounds like the engine is running fine but you are a bit heavy to get on plane. What kind of crud do you have? Around here it would be barnacles which can be a nightmare to clean.

Rene

[TexasLXC275]

The crud on the bottom is kind of a brownish color. Almost looks like mud but it's not.

[Donziweasel]

I agree with Mattyboy. 3100 rpm's even with the crud on the bottom is really low. I am not sure it is a pitch problem, due to the fact that he would have to go down 12-14 pitches bascially to get he boat in the 4600 rpm range. Just my 2 cents after dealing with pitch problems since I bought my 16.

[Ranman]

Sounds like the boat is too heavy or there's too much drag coming from somewhere (bottom condition). Clean the bottom and retest. We can give much better answers with a report after running on a good clean bottom.

[ospreyproduction]

Make one change at a time. The crud must come off first, then see where you are with the prop.

[goatee]

yeah but 15?!??,,,sounds like he's still got the trailer on the bottom.
is also possible previous owner swaped props before the transfer of ownership.

[TexasLXC275]

I just got off the phone with a guy at a Donzi Service shop. His feelings are that it could be a hub. Can anyone shed light on what a hub is? I'm assuming it's in the outdrive somewhere.

[CHACHI]

I just got off the phone with a guy at a Donzi Service shop. His feelings are that it could be a hub. Can anyone shed light on what a hub is? I'm assuming it's in the outdrive somewhere.Rubber hub is in the prop. It could be slipping. Index a spot on a prop ear to some spot on the hub and go for a ride. The spots should not have moved. If they did, you hub is spinning. Ken

[oldandtired]

If your hub was spinning, you would turn much more than 3100 rpm. You can't make any prop determinations until you actually get on plane. A 1/2 inch layer of crap all over a 27' boat sounds like a big enough problem to me. You have a pretty big boat that doesn't have big power. I would be willing to bet that the crud is your main problem. You might also want to check your throttle linkage. Make sure that the throttle plate is actually opening to the full throttle position. I had a friend that was ready to throw away an outboard because of a bad cable. If that doesn't take care of it, then do a tune up, check compression and timing and retest.

Rene

[Last Tango]

All of these are good answers to your question.
Clean the bottom and the prop. While the boat is out of the water, read the prop and see what size and pitch it is and "index it" (mark the prop and hub co-location with permanent ink > test
If still slow, tell us you cleaned the bottom, and give us the prop size.
If prop size is okay or at least within range, then jump in the water and see if your index lines still match up. If the index lines are not still lined up, it could be the hub needs replacement. Pull the prop and send it off to a prop shop. If the prop is the wrong size (too big) then revisit us here for some suggestions on the right size and try one from you prop dealer before you buy.
Bottom is clean, prop is OK? Then you have some issue with the engine. Have your service department check the throttle for full movement, carburator for cleanliness/fuel filter/etc., do a compression check, timing for full advance, plugs. Repair or adjust as necessary.
All this checks out? Carefully remove the trailer from the boat BEFORE you leave the ramp.

[joseph m. hahnl]

Also cover the basics, Like are all the plug wires on? does it have a fouled plug?, The simple stuff that can ruin your day:wink: .



joe

[Avialanche]

I have a 1996 LXC as well, it gets on plane at 18-19 mph.........and tops out at 47 mph at 4400 rpms with Bravo III 7.4 litre carburated engine with no bottom paint or crud whatsoever, just to give you an idea of what your boat should be capable of if the bottom was clean and the engine is running properly.