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Hello, I have just purchased an '83 Bertram 31 and I am planning to fit a Yanmar 315 engine. What should be the correct propellers to choose?
thanks

Welcome!

Have seen Capt. Pat suggesting the following setup:

315's
Trans gear ratio = 2:1
Shaft = 1.5 Aquamet
Props = 20 x 24 4 blade or 20 x 23 4 blade

Welcome to our board here.

As Hueso just answered your question I am sure that you will find the answers to many many more questions as they come up.

You picked a pretty good place to hang out here.

Harry

Kostas,

Hueso is correct. When Patrick and Bruce did my re-power to Yanmar 315s with a 2:1 gear, the four-blade, 20" diameter props were fine-tuned to a 23.5" pitch. The performance curve on my 1973 B-31 Sportfish was as follows:

RPM...................................Knots

700 (idle)............................5.1
2000...................................13.7
2500...................................20.2
2800...................................22.9
3000...................................24.9
3200...................................26.7
3400...................................28.0
3600...................................29.6 (Max continuous operating RPM)
3800...................................31.5 (Max rated RPM per Yanmar)
3950...................................33.0 (WOT)

The factory recommended a slight "under-propping" to allow the engines to turn a little higher than the max rated RPM so with a dirty bottom and heavy load the engines would still hit the 3800 number. That is why they were propped to slightly exceed the 3800 max RPM. Hope this helps.

Tommy what kinda fuel numbers do you get, just out of curiosity.

Matt,

I think it was around 8 gallons per side at the 3000-3200 RPM range when I had her. She's in the Med now, and James says she continues to perform flawlessly (his words).

Hello, thank you all for your answers!
I have another question too: do you recommend to add a small generator or not?
thanks again

The generator depends on your needs. You want 110 0n the boat or AC you will need it. I dont have one. My boat is just 12 volt.

Yesterday I received a message from someone I know saying that I "mislead" another person in Puerto Rico with the information I provided in this post. As it usually happens with dumbasses in blogs, they do not read that these are suggestions not to be taken literally as each boat has particular needs, specially, when you have super heavy boats. Another aspect he should have taken into a account is that the warmer waters of the tropics will automatically affect your speed. I'm venting and sometimes I think is not even worth it.

Kosta hi,

Where are you and where is the boat?

You need 220 volts only if you put AC and a normal refrigerator. If not, youre MUCH better off with solar pannels.

Guess

This was an old post. I would say the person either has nothing better to do or is just out to drive you crazy.

Plus, as we all know you in 99% of the cases,swinging a prop bigger than21 inch's can cause wear on the hull from the prop wash. So they are really playing with pitch and cup more than anything.

Tell your friend to get a life.

Hueso...

When I was a Bertram newbie and started asking questions here and on the B33 forum I took everyone's comments as suggestions and not absolute definite statements.

I have always believed that the captain is responsible for the maintenance and operation of his (or her) boat. I appreciate everyone's suggestions, especially from my brothers here, but in the final analysis, the responsibility for everything related to the maintenance and operation of my boat is mine.

I once heard a yacht club friend who I thought was a pretty good skipper blame a crew member because he ran his boat aground and the crew member was not paying attention to the channel markers... He was immediately demoted in my mind.

I hope this helps. We are also running 1.5:1 gears 315hp Yanmars, 1 3/8 shafts, with Michigan nibral 18x20 djx 3 bladed props in a very light Bahia mar. We have 1450 hours and have had no shaft issues. This setup was recommended to us by Al Grovers Marine in Freeport, NY. The boat turns 3850 loaded at 36.4 knots in the spring when it first goes in the water. She slows down a little bit at the end of the season due to bottom growth. We are averaging 100 gallons of fuel on day trips to the canyon, running anywhere from 70 to 100 nm each way, with 8 hours of trolling. We like to run at 26 to 28 knts, anything more is getting a little
Squirrelly.
That a previous post from Chris Holgerson.
Now with remodel and probably 1000 more lbs rides better with 24-28 knot cruise at 2800-3200 rpm and tops out at 33.5 knots at 3850 at this years sea trial with five guys and 170 gallons fuel.
Interestingly burned 11.5 gph on five hour run from Worton Creek to Indian River at 26-28 knot average very economical. Last fill up averaged 13gph at 3200 rpm run.

Hueso,

After being in the boat biz for 29 years as you know, I can say with all authority boaters as a whole are dumb as a stump. The folks who frequent here are a clear exception to that rule which includes you.

Don't sweat it. Can't fix stupid.

Edited to add: now being in the car business, the same applies there as well.

Edited to add: overall majority of people are dumb as a stump.

Bruce wrote:overall majority of people are dumb as a stump.

You're such an optimist... I can't figure out why you're called the mean team leader <grin>

Bruce wrote:Hueso,

After being in the boat biz for 29 years as you know, I can say with all authority boaters as a whole are dumb as a stump. The folks who frequent here are a clear exception to that rule which includes you.

Don't sweat it. Can't fix stupid.

Edited to add: now being in the car business, the same applies there as well.

Edited to add: overall majority of people are dumb as a stump.

It gets worse when dealing with the current generation who have had teachers who have no idea how to teach.

Hueso wrote:Yesterday I received a message from someone I know saying that I "mislead" another person in Puerto Rico with the information I provided in this post. As it usually happens with dumbasses in blogs, they do not read that these are suggestions not to be taken literally as each boat has particular needs, specially, when you have super heavy boats. Another aspect he should have taken into a account is that the warmer waters of the tropics will automatically affect your speed. I'm venting and sometimes I think is not even worth it.

Hueso-
Goes with the territory Hueso.
Props are that area of boating that people just get stupid...the mind goes numb and dumb. So many dwell on the best performance numbers of this guy and that guy ignoring the variables...they just want faster for free or as close to free as possible.

How many times have we increased pitch, added some cup to a customer wheels as they had 400+rpm over WOT recommendations...to find out they can no longer get up on plane after wheel modification.
They come back irate...we sit and talk again to find out that 400+...well that was on sea trial two years ago when boat had 1/4 tank of fuel, minimal fresh water, holding tank empty, no owners clutter on a freshly painted bottom. Truth later comes out he just about turned up to recommended WOT before giving us props and that 400 may have been more of a 300rpm.

People hear what they want to hear.

I know that there have been many posts and discussions on this subject, but I guess it is rocket science....

These are the readings of the performance of my B31 last year.
2x300HP Yanmar, 2:1 reduction, 4 blade 18.5x18.5, 1/2 load (fuel and water).

RPM KTS
1000 5.3
1400 7.1
1800 8.6
1900 8.9
2000 9.4
2200 11.4
2400 13.2
2600 15.3
2700 16.3
2800 17.4
3000 19.2
3200 20.2
3400 21.7
3600 23.5
3800 26.4
Help!

This year I changed the pitch of the props to 22.5", and saw a very minor change in performance, so at 3,000 rpm 20.2kts and WOT about the same. Max engine rpm was 4,200 last year and 4,100 this year.

If I calculate the propeller slip at 3,000 rpm, 18.5" pitch 19.2 kts = 15.5% (not bad!) and now with 22.5" pitch slip = 27% !!! Am I missing something?

I have compared to other B31 prop data as well and average slip at 3,000 rpm ranges from 13.7% to 19.5%.

If I increase pitch to 25" with 20% slip I should be seeing 22kts. Does that make sense?

Thanks in advance for any input!

Mat

Matt

Interesting numbers. I am running 270 Cummins, 20 X 23 cupped. Not sure of the cup amount. I top end at 2650 and 30 knots. The torque curves are so different since the Yanmars are more like big blocks. At 2200 I am running at 24 knots. I am light, no tower. If I get the wind and current right she will run at 26 knots at 2200.

Tony hi,

Thanks for that info! I am guessing you have 3-blade and 1.56:1 reduction?

I think I should max out at around 30kts. I think my boat is super-light as well (you can see pics from the topic more-than-I-bargained-for Restoration), I am going to have it weighed soon as well.

As you correctly said, the torque curve on the Yanmars is more like a big block, so I should worry about high engine load at lower rpm's I guess...

Anyway, my plan is to have the boat weighed, check the guy at the prop-shop did the correct settings (the pitch is what he says it is), and going by the theory of 1" in pitch is equal to about 1" dia, increase the pitch to 25".

Thanks,

Mat

Hueso wrote:Yesterday I received a message from someone I know saying that I "mislead" another person in Puerto Rico with the information I provided in this post. As it usually happens with dumbasses in blogs, they do not read that these are suggestions not to be taken literally as each boat has particular needs, specially, when you have super heavy boats. Another aspect he should have taken into a account is that the warmer waters of the tropics will automatically affect your speed. I'm venting and sometimes I think is not even worth it.

My reply would have been "Go F@#$ yourself!" As I have gotten older my tolerance for jerks has gone down!!

Matlos

I am running a 4 blade prop.