Speed isuue

1975F26 · Post by **1975F26** » Mon Aug 17, 2009 10:05 pm

Well i am new to the whole inboard motor thing i just bought my first on its a 1975 F26 it has a repowered 318 i just am a little pissed about the spped i need to know if somethins not right at WOT its at 3k and will only do 18 MPh with the current goin out with a back wind also just wondering also is the throttle adjustable this boat still has the original shifter in it or is it easier to ajust the carb

prowlersfish · Post by **prowlersfish** » Tue Aug 18, 2009 6:56 am

Is the bottom clean ?

g36 · Post by **g36** » Tue Aug 18, 2009 7:37 am

is the timing set properly? is the mechanical advance in the disributor operating properly? can you tell if all 4 barrels are kicking in on the carb?

randyp · Post by **randyp** » Tue Aug 18, 2009 2:04 pm

You should be getting 4000 rpm at WOT and top speed of 24 mph (GPS) with a clean bottom, calm water and not overloaded. I can cruise all day at 3200 rpm at 19-20 mph (GPS). I have the single stock 318 w/4bbl carb (which was rebuilt last year). Check the plugs, wires, ignition timing, etc. All of the stuff I just went through will impact speed and performance. The 318 is spec'd at max hp (225) at 4000 rpm. Hope that helps.

randyp · Post by **randyp** » Tue Aug 18, 2009 2:07 pm

Oh...and one more thing. Are the trim tabs operational? Mine blew out last year and it made a huge difference in speed and trim because the stern just wanted to stay in the water no matter how much throttle I gave her. I fixed them this year (simple hydraulic hose leak) and things are poifect now.

1975F26 · Post by **1975F26** » Tue Aug 18, 2009 3:50 pm

mine kinda work what size should i have the tabs on the boat look kinda samll butt by the way the bottom is clean the 4 barrel is kickin on and the advance on the distributor is working fine another thing the previous owner added on 8 inches to the keel for "stability" do you rhing this would affect this

jav · Post by **jav** » Tue Aug 18, 2009 4:02 pm

Welcome to the forum and Trojan family. It's a pretty freindly bunch thats always willing to lend a hand. If I could ask just a few things from you.

1) Please punctuate your sentences and posts. It can be easy to misinterpret things and having one long statement make it hard to read, understand and offer clear advise.

2) provide as much detail as possible. You say the bottom is clean. How do you know that and does this include the running gear? Have you eyballed the props lately? You say the keel was augmented 8".... what does that mean?? Was the whole keel extened 8" in depth or- was the length of the keel extended 8" in length towards the transom? Details are important.

3) Follow-up. Folks will go out of their way to help you. It's nice to have the effort ecknowledged if for no other reason - so the next reader knows the outcome.

MattSC · Post by **MattSC** » Tue Aug 18, 2009 4:55 pm

Do you know what size prop you have on the boat? You could be overpropped, it should be around a 14 x 10 with a cup.

1975F26 · Post by **1975F26** » Tue Aug 18, 2009 5:58 pm

Sorry the whole length of the keel was extended 8 inches down and the prop is a 14x 10 non cupped also i pulled the boat out about a week ago and scrapped the whole bottom of barnnacles the prop had a few nicks out of it i just didnt have the money at the time to replace it but will that really affect it that bad bc i had just drove the boat from Barrington RI all the way to the Merrimack River and the top speed was was 16 MPH 270 miles at 16 MPH takes a damn long time lol

randyp · Post by **randyp** » Wed Aug 19, 2009 8:44 am

If the entire keel was extended 8 inches that would give you a lot of wetted area to lift up and out of the water. As I remember the hull is a semi-planing design, so that extra keel would defeat the purpose and keep more hull bottom in the water versus ON the water. If the RUDDER was extended 8" that might have some effect with extra drag, but would probably not have that much effect. The fact that you can't get up to over 3200 rpm says there's either too much drag, too much weight, or the engine needs to be tuned. You also talked about barnacles being scraped off the bottom - was this BEFORE you took the trip or after?

1975F26 · Post by **1975F26** » Wed Aug 19, 2009 9:41 am

i was just thinking the previous owner replaced the sun deck with 5/4 mahoganoy i belive before all there was 3/4 plywood if there is too much weight would i be underproped would i have to go up on my prop.

jav · Post by **jav** » Wed Aug 19, 2009 10:19 am

Usually when you can't achieve rated RPM due to weight/drag- you prop DOWN not up.

I realize we're only talking but -before you get too many lines in the water and get all tangled up, you should try to get a good grip on where you are.

1. You know you have a speed and RPM problem- but don't know the cause.
2. Folks have asked about speed, tabs, cleaning the bottom/running gear, engine tune/condition and how all that fits together in time. This is very important to understand if we are to help narrow down the probable cause of your problem.
3. There are two key areas of concern- A) Is the drive train able to produce it's rated thrust? B) Is the hull drag normal or higher than expected.

It seems from your answers that both are suspect with perhaps a little more emphasis on hull drag. Clearly- the extended keel and additional weight could have a huge impact on what your experiencing. I'd like to know what the boat weighs at this point and if the keel work/bottom are absolutely fair.

I'd also like to know-
1) did you sea trial this before you bought it and did these problems exist then?
2) If so- what was the explanation then?
3) if not- what changed?
4) are the speeds your giving truely MPH (statutory Miles Per Hour) or are they really Knots (nautical miles per hour)?

The devil is in the details- and you need to methodically provide them if we are to make the most of this effort.