Another Trip

Rodman · Post by **Rodman** » Sun May 09, 2010 9:37 pm

I took another trip in the river this weekend. I left Friday night, stayed until today. It was great time. I had to replace the starter on the hook. But it was two bolts not a hard job. I did take that 14x10 prop and try it. It was a for sure no go. I just do not know what to do. I tried the 14x12 and 14x10 but would not plain out. I did get too 4100 RPMS. The 16x18 prop is lugging the motor. I only get 3100 RPMS out of that prop. She does plain real good with that prop. I got up at 6am and went to the doc so I could try that 14x10 prop, I puttered to the doc at 1300 RPMS, which was a very nice little putter speed. When I put that 14x10 on there she would not do as it did on the way to the doc at 1300 RPMS. Much slower and less responsive. I am at a loss what to do now. what is the normal RPMS on plain? What is too much to where the engine can be affected? Cause at 3100 RPMS temp was runing about 165 If ill post some photos.

Weekend Photos
http://picasaweb.google.com/rodmansboat ... ekendTrip#

This is on plain

This was this morning on way to the doc to change props.

captainmaniac · Post by **captainmaniac** » Sun May 09, 2010 10:13 pm

I am hoping this translates... I have experience with a single engine 28' Trojan and a twin engine 32' Trojan (and a twin engine 26' Four Winns pocket rocket)...

When propped right, you should be able to hit the 'max rpm' for your engine at WOT. If you can't hit max rpm, you are either over propped, or engine is tired, or trim is way off.

Idle should be around 700 - 800 RPM (maybe as low as 650 in gear), and that should give you about 3 mph.

Just getting on plane should be around 2000 RPM for your boat. Speed should be about 10-12 mph (as per the 28'er I am used to). It should start to feel 'sweet' about 2500 RPM.

Around 3000 RPM, you should be hitting near 20. If I remember correctly, my father's 28' (1969 woodie) with single 360 Chrysler did about 15mph at 2500 RPM and added 1mph per 1000 RPM added (to about 3500 RPM - we never did push the old girl beyond that).

Do you have trim tabs ?

Rodman · Post by **Rodman** » Sun May 09, 2010 10:59 pm

captainmaniac wrote:I am hoping this translates... I have experience with a single engine 28' Trojan and a twin engine 32' Trojan (and a twin engine 26' Four Winns pocket rocket)...

When propped right, you should be able to hit the 'max rpm' for your engine at WOT. If you can't hit max rpm, you are either over propped, or engine is tired, or trim is way off.

Idle should be around 700 - 800 RPM (maybe as low as 650 in gear), and that should give you about 3 mph.

Just getting on plane should be around 2000 RPM for your boat. Speed should be about 10-12 mph (as per the 28'er I am used to). It should start to feel 'sweet' about 2500 RPM.

Around 3000 RPM, you should be hitting near 20. If I remember correctly, my father's 28' (1969 woodie) with single 360 Chrysler did about 15mph at 2500 RPM and added 1mph per 1000 RPM added (to about 3500 RPM - we never did push the old girl beyond that).

Do you have trim tabs ?

YES I know how to adjust them with the RPM. so it will nose over and then I will look at the RPMS if it drops ill nose up until it looks good and feels good. ( nose over = bow up, ( I fly private air craft reason for the)

ready123 · Post by **ready123** » Mon May 10, 2010 2:06 am

You said that you tried 14x12 and 14x10 and would not plane out... what does that mean? You could not get up on plane?
Yet your 16x18 got you on plane, that seems odd? So why not try a 16x16, 16x14, 16x12 or any of those you can get your hands on.

Way back Rossjo said what your engine should do... using a 14x10 you should get 4500 rpm as max: .... Can you get that?
If not then in my opinion we should be looking at the engine first before worrying about prop size.... it is either way down on HP or needs to be adjusted to bring it's power up.

If the engine is weak no amount of effort playing with prop pitch and diameter will work.... a boat needs HP to function against water drag. You need to show that you can get max: rpm with that 14x10 prop before you worry about anything else in my opinion.

Then...
You seem to be missing the key steps here of checking for the right prop for your boat.... or I have just not seen this conveyed. In the original post in this thread it is not clear to me if you have achieved that with any of your props.
Step 1...What is the rated max rpm for your engine? rossjo says 4500 rpm
Step 2.. Do you achieve that with the test prop at full throttle?
Step 3.. Keep lowering the pitch till you get the rated rpm at full throttle.

Of course this assumes that the engine throttle and carb are setup to achieve max: rpm and the HP.

What worries me is you are changing pitch and diameter... there should be an ideal diameter range for your boat.. then I would change pitch for that diameter.
eg: on my 318 powered F32 my 3 blade 16x15 seems to be correct for that diameter.
Going to 4 blades I can carry one more inch on the diameter so 17x14 works best.

Could this be the problem....
I seem to remember some talk about a modified strut on your boat.... has that changed the down angle of the shaft?
What is distance from end of shaft to the underside of the hull? How does that compare with other users?

prowlersfish · Post by **prowlersfish** » Mon May 10, 2010 6:30 am

If the boat will get on plane with a over size prop I would not think the engine is weak . can you reconfirm your gear ratio ? and post a photo of your gear . ( something you said you were going to do ) I believe your drive train is not the same as what it came with , so what other boats like your are using for props is not very relevant .

what speed are you getting with the 14x10 and 14x12 at 4100 rpm and 3000 ? what speed are you getting with the larger prop ?

Have you ever checked you tach you see if its right ?

g36 · Post by **g36** » Mon May 10, 2010 7:49 am

have you checked the mechanical advance in the distributor? in my f32 with 318's distributor i found one spring was gone and the other rusted and about gone. the advance was not doing a thing. i was never able to get to max rpms until i fixed this.
sorry to suggest this if you have already checked your timing

Rodman · Post by **Rodman** » Mon May 10, 2010 8:12 am

prowlersfish wrote:If the boat will get on plane with a over size prop I would not think the engine is weak . can you reconfirm your gear ratio ? and post a photo of your gear . ( something you said you were going to do ) I believe your drive train is not the same as what it came with , so what other boats like your are using for props is not very relevant .

what speed are you getting with the 14x10 and 14x12 at 4100 rpm and 3000 ? what speed are you getting with the larger prop ?

Have you ever checked you tach you see if its right ?

With the 16x18 I plain out quick and at 3100 ( Which is max I get ) I am not sure how many mph I am getting with the 14x10 and 14x12 I can get 4100 RPM it will not even get on plain. It feels like the prop is spinning fast and slipping not pushing the boat very well. I will get GPS this week so I know.

I feel the reason I am not getting full RPM ( 4500 ) cause the prop is too large. I will take some photos of everything today and re-post them.

By the look at this wake I am moving along pretty good.

ready123 · Post by **ready123** » Mon May 10, 2010 9:01 am

Looks to me like you should try a 16x12 prop.

Rodman · Post by **Rodman** » Mon May 10, 2010 9:10 am

ready123 wrote:Looks to me like you should try a 16x12 prop.

anyone have 16x12 LH prop?

9rock · Post by **9rock** » Mon May 10, 2010 10:20 am

is the bottom clean

9

rossjo · Post by **rossjo** » Tue May 11, 2010 12:32 am

What engine again - that 14x10 is pretty small - and the boat is only doing about 18knots in that photo ...

I agree with earlier observations that your engine/carbs need tuning ... make sure you get a kit with Viton seals (I feel/sound like a Viton salesman).

Rodman · Post by **Rodman** » Tue May 11, 2010 12:48 am

rossjo wrote:What engine again - that 14x10 is pretty small - and the boat is only doing about 18knots in that photo ...

I agree with earlier observations that your engine/carbs need tuning ... make sure you get a kit with Viton seals (I feel/sound like a Viton salesman).

YES bottom is clean and the engine is a Ford 351 Windsor

rossjo · Post by **rossjo** » Tue May 11, 2010 1:21 am

The 351 Windsor only ran 4100 RPM with the 14x12 - and would not plane out? I would say that you a) don't have enough prop, and the b) engine is not running 100%.

I don't remember what prop calc said - what gear ratio? We'll assume the 351 is 250HP ...

The 16x18 is WAY too big - 18" pitch! - thats why you only got 3100 RPM.

Ready's guess of 16x12 is in the ball park - but we should review the calculations ....

prowlersfish · Post by **prowlersfish** » Tue May 11, 2010 6:38 am

when he gets the gps and posts th speeds we may have better idea . beleave Rodman is runnig more gear then the 1 to 1 the boat came with . ( if I rember right ???) 14x10 would be close if its 1 to 1 .

Rodman what gear ratio did you say you have ?

Did you check you tach ?

MattSC · Post by **MattSC** » Tue May 11, 2010 8:35 pm

I bet if the 14x10 had a full cup, it would make a huge difference and give the proper rpm. Without the full cup, mine behaved just like Rodman described, the prop appeared to be slipping. When I added the full cup, it was like a completely different boat. Based on the 4100rpm you got with the 14x12 If you add a full cup to that you should be around 3800-3900rpm. 14x11 with a full cup might be your ticket