F-28 Performance

shawzy44 · Post by **shawzy44** » Tue Jun 29, 2010 8:53 am

Hi all,

I have been working on restoring the Rumset for the last 3 years, while I thought I had the engine running perfect, this past weekend I was boating with a couple who had a 1979 F32 with 318s. The F32 was faster out of the hole, seemed quiter and was getting much better performance.

We had about the same ammount of water & fuel. My props were replaced at the start of last season to OEM specs -I think they are 14X12 3 blades (photos in my gallery).

Anyhow I am just wondering if the F32 has a more effiecent hull design or if my performce should be a cause for concern.

Example:

Cruising @ 3200 RPM the F32 was getting 18-20 MPH while my F28 was a a mere 13-14 and barely on plane.

I am getting 4000RPM WOT where the F32 is getting 4500RPM.

The F28 seems to really need the trim tabs to get her to plane, just wondering if there are specific engine related items I should be checking to see if I am getting robbed of power. (Timing ect)

Maybe my engines are just getting tired...

jddens · Post by **jddens** » Tue Jun 29, 2010 11:03 am

Hows clean is the hull...sounds like it might need to be cleaned. My 30' Sea Raider performs much like the F32 you mention.....

shawzy44 · Post by **shawzy44** » Tue Jun 29, 2010 11:08 am

Not a hull issue, the boat is in fresh water and we just started the season up here, fresh anti fouling and she's still clean...

k9th · Post by **k9th** » Tue Jun 29, 2010 11:15 am

Sounds to me like a HP issue if you have standard OEM props, similar engines, and similar loading. Doing a compression check on the cylinders will tell you a lot and give you an indication of how near rebuild you actually are.

koviak · Post by **koviak** » Tue Jun 29, 2010 5:36 pm

F32 has a flatter surface at rear of the hull. Also longer hull will have less drag thru the water. That 28 x 12 hull is a lot to move easily thru the water. Could try running longer cord on tabs to extend your surface area. I ran a 76 luhrs 280 with a single 318 and could cruise at 3000 rpm and 19 knots all day.

MattSC · Post by **MattSC** » Tue Jun 29, 2010 7:19 pm

Are your props cupped? Made all the difference on mine, though it's a different model, F-26. If they aren't you'd probably have to drop down to a 14x10 to get back to the proper rpm.

Dreamer · Post by **Dreamer** » Tue Jun 29, 2010 10:24 pm

I'm not sure whats wrong. My 77 F28 runs about 24mph at 3200rpm. My best wide open throttle is 36mph. I also have 2 F28's. The 77 is a little faster than the 76. One has a VC bottom paint, it gained almost 2mph, just changing bottom paint. My 77 has built engines so out of the hole it is faster, but the top end is with in 3 to 4 mph of the 76. They both have the same props.

captainmaniac · Post by **captainmaniac** » Tue Jun 29, 2010 10:27 pm

Weight distribution can also be a problem... how much crap are you carrying in cockpit / bilge area / on platform? The more weight you carry aft, the harder it will be to climb out of the hole, even with tabs...

shawzy44 · Post by **shawzy44** » Wed Jun 30, 2010 9:53 am

Wow Dreamer 36mph! That's AWESOME! I am goning to get my mechanic down this weekend and look everything over to see where/why I am loosing power (vaccum, compression, timing, carbs ect).

The engines were (apparently) rebuilt in 2004 but the boat sat for 3 seasons before I got it... maybe she needs a little more work.

I like the idea of replacing the trim tabs with larger ones...

Thanks for all the advice.

Dreamer · Post by **Dreamer** » Wed Jun 30, 2010 9:00 pm

shawzy44 wrote:Wow Dreamer 36mph! That's AWESOME! I am goning to get my mechanic down this weekend and look everything over to see where/why I am loosing power (vaccum, compression, timing, carbs ect).

The engines were (apparently) rebuilt in 2004 but the boat sat for 3 seasons before I got it... maybe she needs a little more work.

I like the idea of replacing the trim tabs with larger ones...

Thanks for all the advice.

Yea! that speed was with perfect conditions. tale wind, and 1' chop. I use hardly any trim tab. F-28's tend to be a little nose heavy.

shawzy44 · Post by **shawzy44** » Mon Jul 05, 2010 7:11 pm

Ok so I am going to have a mechanic look at the engines. I want to give him a list of things to check. Any help with a list? What should I get him to check?

Thanks!

Dreamer · Post by **Dreamer** » Mon Jul 05, 2010 9:51 pm

shawzy44 wrote:Ok so I am going to have a mechanic look at the engines. I want to give him a list of things to check. Any help with a list? What should I get him to check?

Thanks!

I would say to start with a compression check, then proceed to to a fuel pressure, followed by a timing check. These are the basic things we check at our marina. We always check everyones props and strut bearings at haul out.
Vibration can rob power also. I have had motors that had good compression, but the cam lobes were wore out, and caused a loss in power. A good Mechanic can change your life

captainmaniac · Post by **captainmaniac** » Mon Jul 05, 2010 10:23 pm

If you have to give your mechanic a list of what to check to diagnose your problems, maybe you found your problem - you need a new mechanic! If he can't tell *you* what needs to be checked, don't let him touch them.

prowlersfish · Post by **prowlersfish** » Tue Jul 06, 2010 6:30 am

It is not a engine problem !!!!! your only gets 13-14 knots at 3200 ? well no matter what you do to those engine you still only going to get 13-14 knots at 3200. you could tune them up put a blower on it and get 700 hp out of them But your still only going to get 13-14 knots at 3200 rpm .

unless the engine is missing don't waste you time with a compression check . even if you had 2 dead clyders it will not change your speed at a given rpm. (yes of course it would efect top rpm. )

look else where

pnmudge · Post by **pnmudge** » Tue Jul 06, 2010 8:49 pm

When we bought our F-28 last year, we had a heck of a time getting it up on plane. We did a bunch of things to fix it, so I can't tell you if it was one single thing or all, or a combination of a few, but we cruise at about 14kts (good conditions) at 2800rpm. That's with about 3/4 fuel and half water.... especially the water... since we have two 30 gal tanks back there and water weighs about 10lbs per gallon!

Here's what we did:
- cleaned the bottom -- sheets of bottom paint were coming off and causing a "parachute" effect -- plus we had quite a colony of barnacles down there
- took the super-cup out of our 14x11 props
- adjusted the timing to 4 degrees (one engine was 4, one engine was 0)
- adjusted the relief valve on the trim tabs so that they react faster. I've been told that the F-28's don't need trim because they're bow heavy, but we didn't get nearly the performance we get now until we could get the trim tabs to push the bow all the way down... maybe we need to add more chain to weigh it down up there?

Everything else we've done pertains to our over-heating issue, so that's not relevant.

Hope that helps!