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Old 08-18-2016, 10:36 PM   #17
Al
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City: ketchikan, Alaska
Country: usa
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 1,940
Hi Mr. Baker,
I did visit and read the article and in the past several similar articles that leave me with frustrations. I am flumxed still after reading this one in conjunction of past forum discussions.

I again will use our boat as the example. Factory weight was advertised at 10,000# Now the first head shaker is each owner purchinging this model was given the responsibility for the options of selecting fuel/water tankage, engine selection and gear ration. So it would appear the factor weight as you indicated,really has little bearing on the final first time into the water weight.

Two boats- Ours was equipped with 100 gallon fuel, 48 gallon water. second boat has 200 gallons fuel and 100 gallons water. Our boat had a 700# Perkins 4-154 and the second a 1300# Perkins 4-236. Our gear was 3:1 and the second was 2:1. each with a different weight.
Obviously ours had a large weight discrepancy when compared to the second boat. (Later here you will read of modifications)


Enter the new owner, (me). It was obvious in the first venture into 3 foot seas and 20 knot wind that this boat was so out of balance stability wise as to make me regret the purchase.
After many conversations including the forum, we added 1000# of lead Note, these boats came with 1500 lead incased keels so that is a set factor.

When we changed the 4-154 out for a 4-236 we also changed from 3:1 to 2:1 gear. Total weight change was a positive 700/750# increase.

The prop on the 4-154 (24x16 3 blade) was mated correctly, the engine turned the required 3000RPM at WOT. the max speed at that setting netted a knot and half over the comfortable setting of 2150 and 6.3-6.5 knots, hull speed by calculation being 6.9 knots. ( turning at 2400 gave the hull speed but also a notable increase in cabin sound as well fuel burn. 1 gallon per hour to 1.5 gallon per hour)


We then made a change from the 4-154 as the main seal on these engines and twice changed at $1500.00 on ours, leak and leak badly.) we chose to replace the engine with a 4-236 which added 600# to the mix.

Now here is the rub reflected somewhat in the discussion. We retained the prop (24x16 three blade) from the 4-154 (3:1 gear) and installed a 2:1 gear retaining this prop. The result was a max WOT of 2000 RPM. obviously over propped.
Take you pick, there are three fractory ratings for this Perkins engine. 2500 RPM for continues heavy duty (what ever that means) 2800 RPM for intermendate duty and 3000 for I guess call it 'Light duty" what ever,
we choose to use the 2500 RPM as it represents 2000 RPM the more aggressive application. So- we are then 500 RPM under that number (over propped). By all measurements, we are so far out of wack as to the 'Norm' and yet, yet,
Mr. Baker, all seems to be in tune. We have since the engine swap and the 1000# of lead ingots, added yet another 400# of ingots. Guess what, we are maintain the 6.5-7 knots at the 13.50-1400 RPM with 500 RPM to spare to WOT. It would seem we should be effecting engine failure. yet again, our operating temp is 160 degrees, I am not sure about the exhaust temp, but guessing by conversation, that our operating temp being as low has some equation to any and all temperature factors.
Our fuel burn is 1.5 gallon per hour.
When we tested at WOT 2000 RPM for a period, we met the original increase of 1.5 knots of the 4-154, lots of black smoke, lots!!! And sound, my God! The noise.
With the 4-236 at 1400 RPM out cabin db's is 71 dbs.

In conclusion, while adhering to recommendations such as the site you offer and admitted factors by formulas being subject to question, the actual results as reported should be worth consideration? Would welcome your input on this submission. Where are the results wrong?

Thanks Mr.Baker.
Al


Not choosing to be argumentative, rather, unable to stand by with real life experience that includes so many of the topic related to what is 'Right' and what is 'Wrong'. the 'Gospel' is so many times open to interpretation I suppose.
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