prop size for 1981 f308 also how i got my props off

[GARYGA]

Well I just found out that the 14 in props on my f308 were on their because of the high altitude of where she was sliped at by the former owners, 8000 ft at flaming gorge, whyoming. Im at 47ft on long island ny. the velvet drive ratio says 15.1.2 the engine is (twins) 228 hp 305 mercruiser ( chevy small blocks) 8 cil.

any help will of course be appreciated/ thanks Gary Ga

by the way i was able to get the old props off pretty easily once i used a lil propane torch and a 3lb hammer and then hit between the blades about 5 to 10 hits and then the props poped right off. i didnt use a puller. I did get one little dent from aiming wrong, but then adjusted my aim and all went well..

[prowlersfish]

Gary I belive that boat came with 14 inch props . what pitch are they ?
as far as the gear box the ratio of 15.1.2 makes no sence . I would use the props you have and see what rpms you turn at WOT then have them reworked to get the rpm in range . my F30 (1977) had 1 to 1 gears and 14 X 14 or 14 X 12 props ( I forget ) with 255 hp 351 mercs

[GARYGA]

Thanks paul. I spoke to a man named john today who is with marine tech in pa. He is often recomended by others who use this forum. He said that this boat of mine with the velvet drive and ratio mentioned came originally equiped with 16 in props so i then called this place bossler in ny, who is setting me up with some used props, about 780 for the pair,
I went with this man, johns opinion because he is supposed to have the knowledge. I hope i didnt just spend money for the wrong props. I will be keeping the old props( in good cond) just to be safe.
thanks paul gary ga

[Paul]

Hi Gary,

I hope that you get your prop diameter & pitch worked out without buying too many for testing. Just a word of caution though, using a hammer is not the recommended method for removing props. Even though you may be hitting the prop directly on the hub without damaging the prop or shaft, the impact from every blow transfers directly up the shaft to the thrust bearing at the tail end of the transmission. The components in your transmission are made of hardened steel and cast iron and don't react well to impact. A small crack in a bearing race will soon destroy the bearing.

A puller will keep all of the force involved in removing a prop at the end of the shaft without causing stress farther up the shaft.

Hope This Helps

[jav]

Gary,

I woudl listen to Pauls recommendation unless your eager to spend money twice. Just as a point of reference, I have a pair of 16x15 3 blade props that were tuned and placed in boxes (they are like new) and I'd be happy to get $150 for both of them.... of course mine are just Bronze, not Gold plated as must be the case for $780 set/used. I hope you didn't buy those yet!

As Paul suggested, you really need to fiugre out what your gear ratio is. What you listed "15.1.2" is not possible. It should be a number which may be whole or fractional, then a colon ":" then another number ,which is usually whole. A few common ratio's are 1:1 (read "one to one") , 1.5:1 (read "one point five to one") , 2:1 (read "two to one").

The first number depicts the input RPM and the second the output RPM. So if you have a 2:1 gear, for each 2 engine RPM the prop will turn only 1 RPM (or half as fast as the engine). This data is crucial to correct prop sizing.

Also- prop tip to hull clearance is important and should be 15% of blade diamater. You can go as low as 10% with some increase in noise but 15 is pretty safe. If your going from 14 to 16, you need to confirm you have the clearance.

Paul was right on the money... you should try the boat (fully loaded, with a clean bottom) with the props you have and record speed versus RPM in intervals of 200 RPM also recording maximum RPM for each engine. The boat should be run both directions to cancel out effects of wind and current. Even with all that data, at best expect to get "close" if your making a wholesale change in running gear. Just putting on what someone says is right is really just a $780 guess.

[Stripermann2]

Excellent replies from everyone...

Gary, both Paul and Jav are on the money here. That price for used props sounds very high too. I bought a spare set of 16X16 Nibral 3-blade props, cupped and ready to go for 200.00.

Good luck with the switch.

[prowlersfish]

Jav , pretty much said what I was going to . would like to know what the gear really is .the other Paul is also correct .

I would like to add that even if you got the same props that came on it new they still maybe off some as no two boats are the same . the props that came with it may have been close when new ,but thats was a long time ago . your boat has changed . more gear on board add toys , are they the same engines ? same gear boxs ? alot can change I would see what it runs like now then you will have a base to go by. you may just need to re pich .

aAso you said you needed 16" wheels but never said the pitch ? I hope did not just ask for 16 wheels .

One last thing ( maybe a dumb qestion )what is a F308? I know what a F30 ,F32 and F36 and most others I was thinking it was the same as a F30 But I may be wrong. Do you have a Photo ?

[Stripermann2]

One last thing ( maybe a dumb qestion )what is a F308? I know what a F30 ,F32 and F36 and most others I was thinking it was the same as a F30 But I may be wrong.


Paul, not sure if this correct but my manual shows a model 308 and a 309 both as 30' flybridge sedans. The 308 is a twin and the 309 is a single.

Probably more to it as well...

[prowlersfish]

I know my F36 is a 460 . I have looked at all my trojan info and can not come up with any numbrer other than F30 F32 etc . I know they had the other number ( after the ID # on the hull ) . ever F30 I have seen had 1 to 1 gears and 14" wheels ( less the 1 we put big blocks in ) But then again I have never seen a F30 with a single engine but I know they made them .

I just would hate for gary to get the wrong wheels . I would like to see photos of the boat and gears

[GARYGA]

I hope i learn to blog then listen for a few days, in the future. I assumed the guy from marine tech(john) and the guy on my end at bossler and sweezy (prop people in Long island n.y.) were in the know both advissed me to get the 16's,
I did as i mentioned. now i hope they work correctly. I wont be putting them on until i am off of my lil mountain here and next to the ramp at water. They B & S said they would work with me if adjustments were needed.


patience is indeed a virtue and I am begining to think this boat adventure of mine is here to teach me that.

thanks all gary ga

[prowlersfish]

Gary , I am sure John at marine tech knows what you boat came with .
just becuse the one's I have seen were 1 to 1 gears ,doesn't mean your did as trojan had many many options .and if you do have a reduction gear then of couse you would have a larger wheel like the 16"


still would love to see a photo of the boat ,one on the tow rig would be cool ! good luck and keep us posted .

[prowlersfish]

Gary , every thing I said on prop sizes was wrong as I thought you had F30 like I know . sorry about any miss info I gave .The boat you have is set up a lot different . That is one fine looking boat your have . I would love to see more Photo's . hope you get it in the water soon .

[rossjo]

http://www.BOATDIESEL.com's prop calculator:

10,000lb
27' Waterline length
Twin 228HP engines, 300RPM cruise, 5000RPM max
1.5: gear ratio direct drive

Recommends 14dx13p 3blade non-cupped prop
16in dia prop should be 11in pitch ....

MAX PERFORMANCE
Available Power: 442.3 SAE hp ( 329.8 kW) @ 5000 RPM
Max Speed: 28.4 kts
Fuel: 27 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 111 SAE hp ( 83.0 kW) @ 3000 RPM
Cruising Speed: 14.2 kts
Fuel: 7 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 14.3 in. Pitch: 13.2 in.
Blades: 3 Cupped: No
Transmission Ratio Acceptable
PROPELLER BASED ON INPUT DIAMETER
Diameter: 16.0
Pitch: 11.2
Blades: 3
ALTERNATIVE GEAR/PROP COMBINATIONS
Gear Ratio Shaft RPM Dia. Pitch
1.2 4167 12 11
1.4 3571 13 12
1.6 3125 14 14
1.8 2778 15 16
2 2500 16 18
2.2 2273 17 19
2.4 2083 18 21
2.6 1923 19 23
2.8 1786 20 25
3 1667 21 26

[rossjo]

Oh yeah - USE A PULLER ... No hammering. Slight taps with a brass hammer if the boat is out of the water, but ONLY if the puller won't work!

Rent or borrow a puller - or have your marina do it - but don't beat the props off (please)!

[mr elevman]

if the the boat has a pulpit is it mesered from the end of the pulpit or from the point of the bow