Gas or Diesel ? A Follow Up Featured

Written by Boat Nut Media
Rate this item
(0 votes)

Gas or Diesel? A Follow Up.

 
More detailed information on the boats in response to a readers questions 



Diesel boat details are as follows:
1- Twin Cummins Diamond  Series Inboard 8400 with diesel generator
2-  Vessel weight 28495 lbs
3- 799 hrs

Boat had 1/2 Tank of fuel when departing, and was empty of all but safety gear, no water and pumped out.

Gas boat details
1-Twin 8.1  Crusader motors with gas generator
2-Vessel weight 27495 lbs
3- 65 hours


Boat had 1/2 tank of fuel when departing and was empty of all but safety gear, no water and pumped out

Both boats where side by side when they left and arrived the same way, this was a rare occasion where the two boats where ran side by side all the way. The gas boat set the pace at 4500 RPM.and the diesel matched the pace. The price per gallon of fuel was not critical to the discussion, as we were not trying to determine gallons per hour of fuel burn. It was a general note that the a diesels cruising range based on the same amount of fuel far exceeds gas, as the diesel burnt just about half of the gas boat period. These two boats are rigged with identical size single center mounted fuel tanks.

Water line difference question:

One of the questions was in regard to water line at the dock with no one on board it is obvious that there is a difference as the diesel boat weight is 1000 lbs more than the gas boat.

Does the diesel motor work as hard as the gas motor:

No diesel motors do not the gas motor develops a huge amount of torque when pulling through the RPM range yes, but does not maintain the torque  and hp at the prop any were near were a diesel motor does. Diesels love to be under a constant loadAll boats have hull speed limitations that are available, if you are hitting the max RPM well before the recognized hull speed then you may have the wrong prop package on the boat. That is not the case in this comparison.

What Does it mean when you say diesels are not affected by boat load as gas motors do:

This is in reference to the fact that many times on a boat this size you will add a tender on a bracket of one type or another and the fact is the diesel will not hardly be affected. A gas motor will feel the load difference. Every boat in Canada has a load capacity plate do you know where it is on your boat, if you ignore this plate load limit it will affect any boat with any power plant not just due to motor lag but the hull design can be affected which is a safety issue, so Know your load limit and stay within it. One of the ways to know the true boat weight is at the travel lift most boat owners do not ask the weight of the boat when hauled out.


These boats were brought up to RPM and left there for four hours, and the diesel did need a service, Had it have had the service the smoke may have been reduced however it would have burned cleaner and got better fuel burn. Not all diesels are smokey and smelly as many have under water exhaust this is why I stated that the exhaust set up on this particular boat is poor, but if you think that a diesel has no odor at an idle at the dock you are wrong. Out on the lake or in the open the exhaust can escape away, but against a dock in that trapped space they smell. You know when a diesel starts and is idling if it is backed into the dock which is the way 99 percent of the boats that I attend are moored.


This was a comparison done of two identical boats from the same manufacturer out of the same factory, all original no modifications, Boat Nut Media could get out of control with prop sizes and pitches and wet load weight, but that is not our goal. We try to provide information that is based on facts the way we see the boats and the way they run. This is the way the manufacturer delivered them and that is what boaters really have to deal with.

You can always break a boats running information down into a significant amount of detail, but at the end of the day the boat will do what it is going to do, and I tell it as I see it not every one will like it or agree with it.

Original response from one of our readers:

I only know what I have seen in diesel boats and what I have been involved with on discussion boards such as this.
This is one of the most common ways leading to people ruining their diesels.....
"The last benefit to a diesel is they do not seem to care what you load on your boat they seem to perform pretty much the same way with or without the tender and all your gear on board"
they load the boat heavily over time and overload the diesel engines.
And this way as well....
"This makes for a much smoother ride in the diesel as the running gear is larger you just do not feel like you are pushing the diesel hard at all."
They feel like the diesel are not working hard so they run them to fats and way to near their max rpm's when over propped.
"Both boats were ran side by side down the lake for four hours on plain. The gas boat burnt $400.00 worth of fuel and the diesel burned approximately half of that $220.00."
This tells us nothing about fuel burn rates as fuel prices are different in various places. around here the price of gas is typically 10-15% more than diesel fuel at marina docks. The 41 Silverton we cruise with typically gets about 0.5 nmpg at its cruise of 15-16 knots burning over 30 gph at those speeds.
"So the weight difference is mainly in the motors themselves. However we will say the gas boat sits approximately two inches higher than the diesel boat at the water line."
There is no way to know which diesels are in this boat but we know they do weigh more - even if they weigh a combined 1,000#'s more than the big block gas engines there is something really wrong with a 2" difference in hull height. As a comparison I can take on 400 Gallons of fuel and 200 gallons of water and that only affects my height be about 1" (about 4,500#'s). What 41" boat goes down 2" at the water line when 6 adults or so have boarded?
" At an idle at the dock the diesel can be dirty and smelly, as a matter of fact other boaters were not happy with long term idling"
We have commonly been on raft-up where more than half a dozen larger diesel gensets were running and there was no noticeable smell.
Similarly when the boats come in to tie up and the mains are running (various brands) there is very little noticeable smell.
I am guessing there are some other issues with each of these boats which may affect comparisons of individual differences. Engine condition, prop sizing, prop and running gear condition and boat loading all can make a very large difference. Running any side by side comparison is hard even wen you know the boats engines are well tuned and each boat is evenly loaded and in good shape.
Hope this helps

Thanks again for the comments they are great. Again I am not an expert but I would ask the following:they load the boat heavily over time and overload the diesel engines. Is this overloading only an issue with diesel owners or is this more of a problem of boater education ?They feel like the diesel are not working hard so they run them to fats and way to near their max rpm's when over propped. Same question as above. Does this really invalidate the comparison or is this more an issue of boater education ?
]
This tells us nothing about fuel burn rates as fuel prices are different in various places. around here the price of gas is typically 10-15% more than diesel fuel at marina docks. The 41 Silverton we cruise with typically gets about 0.5 nmpg at its cruise of 15-16 knots burning over 30 gph at those speeds. Since the claimed fuel consumption is about 50% less to travel at the same speed and distance does it really matter what the cost of the fuel was. What if the test was done when the prices were exactly the same ?There is no way to know which diesels are in this boat but we know they do weigh more - even if they weigh a combined 1,000#'s more than the big block gas engines there is something really wrong with a 2" difference in hull height. As a comparison I can take on 400 Gallons of fuel and 200 gallons of water and that only affects my height be about 1" (about 4,500#'s). What 41" boat goes down 2" at the water line when 6 adults or so have boarded? A good observation and you are right more information would have been good. But the same question. Does this invalidate the comparison ?
We have commonly been on raft-up where more than half a dozen larger diesel gensets were running and there was no noticeable smell.
Similarly when the boats come in to tie up and the mains are running (various brands) there is very little noticeable smell.
I am guessing there are some other issues with each of these boats which may affect comparisons of individual differences. Engine condition, prop sizing, prop and running gear condition and boat loading all can make a very large difference. Running any side by side comparison is hard even wen you know the boats engines are well tuned and each boat is evenly loaded and in good shape.
I guess everyone has their own experience's in terms of the smell of diesel boats. But you make a very valid point that if they are not properly cared for the issue can be much worse.

We would like to thank our readers for their comments and questions, as this is exactly what we were hoping for. We wanted other boaters, technicians, and manufacturers to voice their opinions, and share their experiences. After all we are a boating community and should all have a voice in it.


Copyright 2015 © Boat Nut Media, Toronto, Ontario. All rights reserved. No part of this information/publications may be stored in a retrieval system, transmitted, or reproduced in any way, including but not limited to photocopy, magnetic, or other record, without prior agreement and written permission of the publisher, Boat Nuts Media ©™ No liability is assumed with respect to the information provided.
Read 2289 times